My Dad's Poa Wants To Buy His Property

My father is currently in a memory-care facility and is nonverbal.

It is stipulated in his will that upon his death, his three children will split his assets equally.

His property is assessed at approximately 790,000$. We have borrowed about 100k against it to pay for his care, and are about to have to do so again.

I have two siblings- a brother and a sister. One of my brothers is his financial PoA. He is proposing to buy the property for 450,000ish. The idea is that he would put that money into an account that would be used for Dad's care.

When I suggested that the three of us need to have a discussion about it, my brother blew up and basically called me an idiot for not letting him take care of Dad. My position is that we are taking care of him, and that taking care of Dad also includes getting a fair price for his property, to insure that we can afford at least 5 more years of care if he needs it.

My sister and I are now concerned that our brother will act unilaterally. My Dad and brother both live in Ohio. I live in California, and my sister lives in Virginia.

I guess my questions for y'all are: am I wrong in thinking that he may not properly be doing his duty as a fiduciary? Is it even appropriate for a PoA to sell a principal's property to himself without listing it or entertaining other offers? Are my sister and I at the point where we need to be thinking about having formal discussions with lawyers?

I appreciate your attention in this matter. Thanks in advance.