Is there a requirement to speak with family members?

No, you don't need to talk to them. If your POAs are invoked, your not allowed to tell them anything. Its between you and Dad. If he wants them to know, thats his business. Its none of his siblings business what you do as his POA. When they call you tell them you cannot talk to them. Get their info from Dad. If they are persistant, fib and tell them you have talked to a lawyer and have been told you cannot discuss Dads finances and Medical with them.

Financial POA is the important one. It can be immediate (as soon as Dad signed the POA) or it needs a doctor declaring Dad incompetent. Medical, even if Financial is immediate, Medical usually needs a doctor to invoke it.

The only responsibility Medical has is to make sure the principles wishes are carried out. Also, to make decisions for principle if not covered in the MPOA. You also talk to Drs and nurses. If Dad is competent, he makes his own decisions.

If I were you, I would speak to the aunt's and uncles once. State your position to them, as you have to dad. That you're going to relinquish POA and have the state take over his care if all this bs doesn't stop immediately. Dad has dementia and is no longer capable of reassigning POA at this point (most likely, but they don't need to know that), so here's how the cow chews the cud, folks. Either dad takes the medication AND stops the accusations of theft, becomes easier to manage, or you and bro are resigning. Then everyone will know, everyone will be on the same page, and maybe, by some miracle, dad's siblings can make him understand what needs to happen. At the very least, dad is facing being moved into Memory Care Assisted Living soon.

And no, you don't have to talk with the siblings. They just might hound you to death until you do, though, if they're anything like dad. And if they believe the rantings of an old man with dementia, they need their own heads examined too. J/s. 🙄

If the issue is dad hounding THEM, all they have to do is block his number, for petesake.

I hate dementia with every ounce of my being, and how it not only ruins the patients life, but SO MANY OTHER LIVES in the path of its destruction.

You are not obligated to talk to Dad’s siblings .

Tell them you are sorry that your Dad is calling them , however you are not willing to discuss details of his condition or care.
Then stop answering their calls .

No I don't think you do. My brother is POA and I do all the work and we don't speak to each other, but that's a whole other story, but honestly I don't see that your obligated to speak to them