Is it legal for my sibling to remove me as POA?

Call Adult Protective Services and also report the attorney to the local bar association and your State Bar.

No, not at all! Only your mom can do so, but not your sibling.

If you and your sisters equally have POA responsibilities legally, I question how your sister(s) could make these decisions without your input / legal agreement.

You may need to hire your own attorney or certainly contact the attorney/'friend' who your sister/s are working with to re-write it.

It sounds to me that you DO NOT have the legal authority you believe you have.

While I appreciate you coming here for a response, I wonder why you didn't immediately call an attorney or the attorney your sister(s) are working with first to clarify what is going on and your rights as a POA (and how these legal responsibilities are split up among the family)

Do you realize this is a legal issue that you need to address? It sounds to me that you do not have the legal authority to make the decisions you presumed you had, otherwise your sister(s) could not do this without your consent. Gena.

Get past the hurt and get real. Hire an attorney for yourself asap to help you navigate through this. Since your mother is unable or incapable of making decisions for herself, then she is not legally able to sign any documents that would be legally binding. Your sister is trying to scheme something and it sounds like she wants your mother's finances.

I am not a legal expert, but I question how your sister can make a trust for your mother's estate naming your sister as POA, which would require your mother signing the trust. So, once again, if mother not capable of signing, I am not sure how your sister could do this.

Also, when you say you and your sister share POA responsibilities for your mother, does that mean you were both legally named POA for mother via a POA legal document or are you both just acting in such capacity?

If your mother signed a new POA (with only your sister as POA), your mother could have revoked the previous POA (with both you and your sister as POA).

Is that legal?

It all depends on whether your mother really isn’t able to decide for herself. (For example, it might be your opinion that your mother isn’t able to; but it might be the law’s opinion that she can). Only a court can decide that someone is mentally incompetent.

Often, the standard to allow an elderly person to sign documents is quite low:
…They just need to be able to know their name, address, birthdate, etc.
…They need to understand what they’re signing.
…(The fact that one has memory problems can be OK).

On the other hand, if your mother was wrongly pressured/influenced by your sister to sign, then that can be elder abuse.

I would need more information. When my parents had to be moved by me due to poor health I was made sole POA and we had Trust Agreements between all of us. Mom and Dad for each other and Trust Agreement between me and each parent. This was to insure their estate dis not go into Probate

Dad died last September and Mom and I got a lawyer to create documents to ensure her estate did not go into probate.

The Trust agreement ensures that I can make sure the terms of the Will are carried out in a timely fashion. I do not have access to funds etc. I will be able to ensure the assets are distributed according to the will.

If Mom was not cognitively impaired she has the right to change her POA. If she was impaired then that is very shady on sisters part and the lawyer

Call that lawyer friend and tell them everything. That you don't agree to be removed and weren't consulted. Do that asap