My only sibling who is co-agent/co-executor, refuses to communicate or provide any information or even answer a simple question. Any advice?

You have a right to know how Moms money was handled prior to her death. My Mom was in an AL and then LTC for over a year and I did not spend $500 a month on her. She had a small pension of $200 I cashed monthly and spent on her needs. Sometimes I had money to roll over. Her biggest expense was Depends. She ate her 3 meals in the dining room. Her Dementia had gotten to the point, she didn't go into her frig or cupboards. She was in the Common area most of the time.

Did the POA say he could be paid for his services? If you find the answer is no and

LTC, all I would have had to provide was clothing and shoes. The toiletries I provided they chose not to use. The facility provided them. They provided the Depends.

You need a lawyer to write your brother a letter telling him he needs to provide an accting of money spent while acting as POA for Mom and Dad. Maybe attaching bank statements with questioned charges highlighted. Maybe call the bank and ask for copies of the checks.

Did his POA read he could be paid as POA?

If you & sibling cannot communicate on your own, I would try for some form of legal mediation to arrange & be present.

So both sides can voice concerns & discuss in front of a third party. In person being 1st preference, then video call, then conference phone).

I am sure it is not easy being the out of state person kept in the dark. I am sure it is not easy being all the boots on the ground help either.

It may take more than one appointment to hear each other. To reach a direction/solution.

I would think leave out in-laws (if no legal reason exists for them to be involved).

You want less drama. Less 'us & them'.
More, 'let's sort this out'. Sensibly.

"Full service" managed care does NOT include MANY things such as clothing, toiletries, shoes, incontinence supplies, snacks, extra foods, the list is endless really. One day I had to go to the store and buy my mother 6 pairs of shoes just to find 2 pair that fit her and that she would keep, then I had to return the others. Then I had to go back to the store for different socks to see which ones would fit her swollen ankles, then wind up buying very expensive diabetic socks from Amazon instead. Then off to the specialty shoe store to buy a certain pair of shoes that would fit her feet to the tune of $90 not including tax. This was ONE day in my life. Then there was the day when mom insisted ALL of her expensive nightgowns from Kohls were 'missing' and she was sleeping NAKED at her Memory Care ALF. Since they were in lockdown mode due to Covid, I could not go there to see for myself what was going on, and had to go to Kohl's and purchase her 4 new ones to the tune of $156.00. The bra debacle is another story for another day.

I went through my mother's money like a hot knife through butter during the last year or more of her tortured life, but thankfully, I didn't have to answer to anyone demanding to know where and why every penny was spent. As an only child, it was only ME responsible for everything, including all the chaos involving hospice and spending almost every waking moment at the ALF with mom while she was under their care, making decisions on her behalf, etc. Each time hospice was on board for each of my parents, it was a dreadful time in my life.

You've been 'out of state' the entire time your sibling has been dealing with the chaos that goes along with managing a parent's entire life, and now you're firing off questions at them asking about how they spent money hinting around like they are a thief?

Call a lawyer.

I would look into a forensic accounting. I do spend money on Mom for groceries, flowers ec at the grocery store because she doesn't love the food at the facility.

if supplies such as diapers, wipes etc were being purchased that could explain the cost

You need to have a lawyer contact the sibling starting with a strongly worded letter asking for answers and going from there

This is a lawyer question not a forum question.