What do you do when parents with dementia living alone ask for help from controlling sibling?

Atagonistic sibling who refuses to communicate with POA and finances
leaves parents (91) without food or care. He already has legal advantage
and all documents hidden at his home. They refuse to call him.
He refuses to respond to calls and e mails. I have provided food and care
for months. I know have enabled the situation. My personal family budget is strained to seek expensive legal advise which my brother is getting from dad.