I recently obtained POA for Mom. Does my brother have any legal rights to see the POA and be making financial decisions on her behalf?

No, your brother is not entitled to any of your commission.
No, your brother is not entitled to any proceeds from the sale of house.
No, you do not have to disclose anything to brother.
You as mom's POA have the responsibility to act according to the POA document. As POA, you act for mom because she gave you that authority. Mom's finances are not anyone's business.

He's only entitled to whatever mom leaves him in her will AFTER she dies, if there's anything left.

Unless he has proofs of financial abuse, he's got nothing. No decent lawyer is going to take his bogus case.

If he manages to get a lawyer, you should find yourself one as well, and pay with mom's money, not yours, because you're doing it to protect mom's assets.

No. He does not have a legal right to be told, shown, or kept in the loop about anything unless he too is named as a POA.
He cannot make any decisions on your mother's "behalf" if you are the one who has her legal POA to make her financial and healthcare decisions. Your brother has no legal right to anything while your mother lives and your POA is valid.
POA expires when a person passes away though. If your brother is named in the will as an heir, he will have a right to whatever his inheritance is if all of the money and proceeds from assets did not go to the care facility.
Unless his name is on the POA documents, you do not have to show him anything or explain anything to him.
He is as they say, blowing it out of his a$$ because there is nothing he can legally do.
You however can make your life a whole lot easier and show him your paperwork. You should. Make him a copy to refer to for the next time he wants to run his mouth and make threats.

I was in the same situation, was POA, sought legal advice, and was told that I don't have to share any financial information and could make independent financial decisions. I was also advised to keep track of all expenses (within reason) to ensure there were no claims of financial irregularity.
With that said, I wanted to maintain an amicable relationship with my brother so agreed to the following:
1. I would send him a quarterly review of the finances. I just take a picture of statements.
2. As there were other incidental costs outside of the cost of care, I would pay myself $250 a month for incidentals. This covers things like her clothes, favorite foods, etc. As these are usually small amounts, it was easier for me to just pay these, rather than track everything down to the dollar.
3. I provided him with a forecast on how long her money would last and what would happen if she ran out of money. I did this as I wanted him to realize that care is incredibly expensive and it is unlikely he will get any large inheritance. We have already spent over $200k on care and any inheritance is dwindling quickly.
I put all of this in writing and had it notarized.

In regards to getting commission for selling your mother's house. He has no right to say anything providing you are paying yourself a market recognized commission. You are doing your job, for which you are trained. You will do a better job than anyone else selling your mom's house as you love your mother and want the best for her. You can seek legal advice, but legally you have a right to work, do your job, and get paid accordingly. I can guarantee your mother would have selected you as her agent if she wasn't moving into memory care.

The only red flag I see is you acting as the realtor in selling your Mum's home.

That is a definite conflict of interest. If you were not Mum's POA, it is just bad taste to benefit financially as her daughter, but as POA you have a fiduciary responsibility to not profit from your POA duties.

I suggest you talk to the lawyer who drew up the POA documents and figure out how to fix this asap.

I have dealt with the exact same thing that you are going through. My brother refused to help with moms care or to maintain her home, but as soon as there was money involved, he got all indignant. I would go to an elder lawyer and set up a trust with moms money from the sale of her home. Then set up a second account as the trustee to the trust. Whenever moms rent is due at assisted living, as trustee you will move money from the trust into the separate account and pay her rent from there. Everything is traceable and trackable.

You get to see peoples true colors when the chips are down...but my guess is you already knew this about your brother. I certainly knew it about mine.

My advice is to continue to make good decisions and care for your mom and ignore your brother. If he has the money and the gall to haul you to court, just take all of your documentation and simply tell the judge that things are being managed for your mom and your brother is unaware of all the details because he has chosen not to assist.

You don't work for your brother. He has three options...he can help and therefore be in the loop, he can say thank you for all that you are doing or he can shut the hell up.

You need badly now to see an elder law attorney. Do not take advice on a forum about financial, medical nor legal things. Recently a commenter here named "Bobby" said we often neglect to say this at the TOP of our response. So consider it said. I am concerned how much you don't understand about being a POA while you are acting as one.
That said, no, in my humble opinion, he has no rights, but that doesn't mean he can't make accusations without any basis in fact. He can accuse you of elder financial abuse and take you to court. Your Mom's estate, as you are now managing it, pays the costs IF/WHEN you win. He has ZERO right to her financials and in fact YOU have a FIDUCIARY DUTY to your Mom; YOU have NO RIGHT to share her information without her competently given permission. As your Mom is not competent you cannot get a competent permission to share.
YOU should not be the realtor in this sale. PERIOD. Any commission you would get as realtor is self-enrichment on your Mom.
You badly need to see an elder law attorney. Again, you cannot guess on these things. The Fiduciary duty of being POA is considered by the court almost a sacred duty. Not knowing is not enough of a defense.
While you are serving as Financial POA have you been keeping meticulous records of every penny in and every penny out? Files? Can you law these before an APS person who comes to investigate you if your bro reports you? If so they will tell him he has no case and advise him against suit almost certainly. Again, hire a realtor. Sell at best price. Get your Mom great care, and be proud of your service to your Mom. Tell bro to go pound sand. That not only WILL you not show him anything, but you would be violating your POA to share your Mom's personal information with him.
And no, of course he doesn't get a penny. You could be sent to jail for giving your Mom's money to your brother. And for taking it yourself.
If you don't know that, then, again, it is very important you see a lawyer to understand your duty as POA before you go any farther in all of this. SEE A LAWYER.
I agree with JoAnn that there is no harm in showing him the POA. But check that out with the attorney as well. But I REALLY agree with her that you do NOT have a right to be the realtor on this.

Polar is so on point. Get an attorney if you must but for the rest, brother can suck eggs.

Sorry it is late but I will be a little more polite. Your brother has no say to anything covered under the POA or how you help your mother under it. Hold your head high knowing you are doing right.

I feel there is one point of contention in your comment "he found out that I recently obtained POA".
After 5 years, one must ask why this wasn't arranged/discussed at the outset when mother may have had more of her faculties to make the appointment with some conviction.

Of course you have been making sacrifices to care for her, but perhaps raising this with your complacent siblings prior, and using this argument to support your intention to become POA, could have been better received or at least given them right of reply. They would be feeling you have gone behind their backs (conveniently ignoring your contribution, no doubt!).

Since mother may not have been of sound mind, it does raise concerns, and despite your being the caregiver (albeit at the behest of your father), it isn't quite the same thing as the appointment dictates.
The tricky thing is how you managed to legally manage your mother's affairs before you obtained POA - and this may be the essence of brother's protestation.

I certainly don't believe you have taken advantage of the situation, but it is important to follow due process and meticulous records need to be kept for any impending inquiry - including the 5 years beforehand where your authority may come under scrutiny.

The issue over commission is valid - not that you owe him half, but it may be wise to engage a different agent to objectively obtain market value without blurring the lines. For instance, if you sold your own house, would you consider the commission as yours and not added to the proceeds of sale? The link to family makes this a delicate area to navigate.

While I agree that you can dig your heels in and stand firm (and I wouldn't blame you for that either), it may only be inflaming the situation.
As family, I think they are entitled to a copy of POA, and in a show of good faith, it would be helpful to advise house sale receipt (would mother have divulged this information in happier times?) and any significant financial changes that have been made - accountability should provide reassurance.

There is a certain duality in being POA - as family, you want to do the best you can to ease the burden; but as POA, you are an agent selflessly and objectively acting as mother would have done were she capable, irrespective of the conduct of her children.

the first thing is to talk with an elder care lawyer about your situation - that person can advise you as to your local/state requirements. You might also talk with your local department of aging about your situation. Make sure you have a copy of whatever documents you have - POA, Will; ETC - preferably one with actual signature. Your brother can make any threats he wants, but that does mean he can get anywhere. I would tell him to talk with your lawyer about what he wants and let the lawyer respond. Telling him that will probably make him back off, but don't let him intimidate you. He sounds like a bully,

See an elder care attorney to make sure your realty situation is on the up and up. That screams sketch y to me. Once things are in order, tell brother to go get his attorney and really you to court if that's what he feels he's gotta do and he'll be paying not only his attorney but all court costs as well as yours because you will not allow your mom to pay for such ridiculousness.