Am I required to give full disclosure of all my mother's finances over the past 3 plus years now that she has passed to my 2 sisters?

If your wife has POA then she is in charge of all incoming and outgoing monies.

She does NOT have to share anything with her sisters. Legally. Morally, another story.

My DH just finished his run as his mom's executor. He kept a spreadsheet of all expenditures and income. He shared it with his sibs. They worked together to sell things, clear the house, etc.

He full well knew he didn't HAVE to tell his sibs anything, but he chose to.

Actually, since her death, POA ends. Who is her executor? If it's Rebecca, then she goes on as before, paying & clearing up debts & selling properties, etc.

At this point, POA means nothing. When the estate is liquidated, all the money issues should come out and be addressed.

Inheritances are paid acc to the literal will of the person who has passed. My BIL did next to nothing for either his mom or dad, yet inherited the exact same amount of money, since that's what his parents wanted. It doesn't matter how much one person has done or not...it's all about how the will is stated.

SHORT ANSWER? No. Of course not. That is your mother's private business. You not only don't have to, you should not. It isn't their business.

All right. The details of who did what and who wants what is totally irrelevant here. What IS relevant is this:
1. In order to confer upon someone a general power of attorney (NOT a medical POA which is what I assume the doctor wants; the MPOA would handle medical and the general POA trumps everything else and is financial, placement, basically EVERYTHING)--repeat: in order to confer this upon someone the "Principle" must be competent to understand what she is doing. This will be done BY AN ATTORNEY in the attorney office and the attorney will examine mother to be certain she is competent to do this.
2. It is the MOTHER who chooses who will be the POA.
The person who is chosen to be POA must understand fully the tasks involved including the need for meticulous record keeping of every penny into and out of every single account, and etc. If the POA need the help of an attorney the elder's assets pay for this expert legal advice.
3. The POA is not free to and should NEVER discuss with sisters or with anyone else any details of the mother's finances. This is not right. This is private information of the mother's and only she or her agent can choose who to share it with as necessary and it should not be shared unnecessarily.
4. If the sisters have a problem with the general POA they are free to hire their own attorney who will go to court and ask a judge to examine the records of the POA. These records will NOT be shared with the complaintant. But they will be checked to be sure they are being kept. The sisters will pay for this attorney and will learn nothing of mother's private information; they will learn only whether the POA is keeping good records.
5. A Medical POA is called MPOA and that person makes MEDICAL decisions when the principle cannot make them any longer, and only then. They make them to the best of their ability to understand what mother wanted. They are free to share or not share with sisters. If the MPOA and the GENERAL POA are not the same person that's not good, but in the end the general POA holds the purse-strings and hence the decisions when mother cannot any longer make her own.

I hope this is kind of a POA 101 briefing outline here.
But you should see an attorney to do this, do not pull stuff offline in terms of forms and have them notarized. That is not good enough for banks and they will turn you away.
This is a HUGE JOB. Be sure that you want it. If you do not want it be sure someone else is capable of doing it.

These family squabbles in which a living parents is caught in the middle between siblings at was drives me, to be honest, frankly MAD. It is the WORST TIME, when the elder is aging and weak, for the family to divide and go to war. It is sad. It is cruel. It is to me reprehensible, and whomever is responsible for doing it? Well, I honestly cannot be honest.

I wish you luck. This is an enormous learning curve. If you take it on you are responsible before the law for this fiduciary duty and to do it well; I wish you all the luck in the world, because it was being made general POA and Trustee for my brother that sent me REELING into AgingCare Forum 5 years ago, frantic and anxious as the cat on the hot tin.
Good luck.

My advice is have an attorney contact available because I had to handle a decade long probate case and that was the absolute pits. All it takes is one person to screw it all up and this sister sounds like the one….

Get legal advice to navigate this.

They might if one of these Sisters is the named Executor of moms Estate & gotten Letters Testamentary showing that. Or 1 has proactively hired a probate atty that does litigation and there actually is an “estate”.

So mom is dead, right? And mom long ago sold her home as she was either living with you / hubs or that daughter in FL, right? So all mom could have had is $ from house sale, savings and her mo income?

Has / Is probate going to be opened & is there a valid will? Like are there actually assets that need NYS probate court for them to be dealt with? If so whomever named to be the Executor is the person who has to deal with all this IF probate is opened.
Otherwise imo it’s all a lot of noise and a buttrash of bother.

Ive been an Executor more than once, and sat in more than one courthouse….. one thing that holds true is that the will is more often than not an “artifact”. It is a representation of what their life and finances were at that period of time. And family and supposed be airs have had expectations that they are due a lil windfall. But life and its co$t$ go on. The elders life, especially their last decade or two, is nothing but outflow for $ & assets. If their only income is SSA retirement income, that is maybe 30K a yr. There sadly ends up very little left of value to place into an Estate left once they die.

Let go of the “who did what” it’s in the past and doesn’t matter anymore. POA doesn’t matter also, it ends with death. I was my dad’s executor and as such didn’t have to explain anything to my siblings. I chose to hire a lawyer to distribute money, didn’t have to, but wanted my hands off it. He wrote letters to them both spelling out what they were getting, neither were given information on what anyone else was getting. It worked out well

Sorry, I totaled missed that mom is now gone. She died.
No, you don't owe anyone anything from the past. Just ignore such requests.
What IS owed not is that the executor, whomever that is, carries out the will as it is written.
Hopefully that is being done.
The rest is he-said/she-said and total nonsense.

Watson, so she died without a will? Then it’s an intestate death.

just what precisely has to - HAS TO - happen is dependent on her State of legal residency laws for heirship & probate. Imho intestate is not ever a DIY has it will have a defined timeline of Notices to be placed & multiple times, affidavits filed by non family as to accuracy, info on the parents past for marriages, divorces, kids, even if they predeceased her.

Its probate lawyer work but often intestate is done by an atty who only does those as it’s its own expertise. Should cost less than regular probate as so much of this is WFH research and filing via the attys bar card to the online portal for the County. Maybe 1-2K + filing fees if the folks were not married / divorced / remarried & did not move to other States in the past. Now If all that exists, it gets involved & more $ as every location where they (mom & dad) lived and could have owned property or appeared on marriage / divorce filings - in my understanding- has to have Notices placed in those local newspaper & more than once.

Any of the siblings can pay for atty to do this. Intestate is equal opportunity for a supposed heir to take on Executorship. Those 2 sisters cannot make you be the one to take this on and pay for it.
fwiw intestate tend to end up run under “Dependent Administration” which means most actions have to be reviewed by the court in order for assets to be sold, transferred or distributed.

If Mom has an estate and no Will your wife can become her Administrator so she can handle Moms finances, like paying bills. As a POA wife cannot discuss finances with anyone else. Its between you and the principle. You stated that wife was made POA because MIL did not want the other sisters to knowher finances. Once the Administrator has done their job, then the State determines who inherits. In your case, Moms 3 daughters.

Are they requesting or their lawyer. Without a Will I don't think it matters because the State will make the final decision.