Elder abuse accusations by estranged children.

More info would be great.
But
If they have filed a formal complaint with APS then there will be an investigation.
If there has been no abuse (that can be financial, verbal, physical, psychological) then you have nothing to worry about.
If they are just spouting off then ignore them. do make sure that all your legal "ducks are in a row" and you can legally make decisions for him.

What is your question? You'll need to provide details and more context in order to receive decent advice.