My brother or sister-in-law typed up a will with state heading. Is this legal?

Holographic (handwritten) wills are valid, as long as at least two disinterested witnesses prove its authenticity [or the number of disinterested witnesses required by the State].

Sounds like your Mom's Will is not valid since your brother and his wife, who will inherit from the Will, were signed witnesses.

Best to verify this is an Elder Law Attorney.

Curious, why did you feel it was important to mention that your brother has Parkinson's?

Is your brother diagnosed with dementia or just Parkinson?
Only about 40% of PD develop dementia.
To me it will be immoral and influencing if family is involve. Any will should be strictly personal decision.
Holographic will is valid, yet, could be easily contested.

The will should never be made under undo influence, courts can nullified it, if proven. Mom being of sound mind should make it on her own.
In fact, I don’t even care or have rights to see what my husband put in his will.
However, in Canada, if somebody just makes a will on napkin and as long as signature can be verified it is legal.

Your first post was from Aug of 2021. I can't remember if you live far away and if Mom lives with Brother. But I do know this thing with brother has gone on for awhile. I am sure you have been told many times that if Mom is competent she can revoke her sons POA and now make up a new will which will revoke any wills prior.

If you live far away, you need to get where Mom is and get her to a lawyer. The lawyer can ask brother for an accting and have him held responsible for any wrong doing. If Mom is of unsound mind you can get Guardianship. Your brother is going to get away with what he does because nobody is stepping in to protect Mom.

Wills require certain provisions, and very specific execution, with the testator/testatrix 's signature being witnessed and notarized. Did this happen?

Comments by others here also address the issue of validity, especially those on self enhancement.

Aassuming your mom is competent, I believe the will is valid. That said, I have heard that if a beneficiary (or their spouse) witnesses a will, the court may void their right to their share of the estate, while the rest of the will remains intact. This may vary by state. Good to check this out in your state.

Banks don't authorize wills.
You cannot witness a will that you stand to be beneficiary on in most instances, but a typed and signed will is a legally document if properly witnessed in most states. Will forms can be got right off the internet.
Does your Mom have dementia? Wills cannot be made out by those suffering dementia.
Again, if you suspect elder abuse ask APS to open a case.

Did Mom already have a will? If not, this could be tougher to challenge, but you would have a case to challenge this holographic will no matter what. You'd need to know what Mom's intentions were before this will was made.

Also know that challenging wills is expensive, so decide if you really do want those antiques. They aren't worth anything these days.

No one authorizes our wills but ourselves. However, there is a reason it states being of sound mind at the very beginning, it is required that she have testamentary capability or she is not able to create a new will.

Does she have an actual diagnosis of mental incapacity?

Also, a POA CAN NOT do anything that enriches them as the fiduciary, it is a violation of their power and illegal.

I have to tell you though, antique furniture doesn't really have much value anymore, unless it is museum pieces. The next generations are into disposable furniture, you know IKEA.