My sister and I had a POA for my dad. Which stated he could not sign anything without us both being there. My brother told him that we were going to put him in a nursing home and the paper (deed to the house) would stop us. My brother manipulated dad into signing it. Is there anything we can do. Dad is no longer living.

First the POA does not sound legal, a POA only gives the other person a right to sign for another person, and the person who gives it, can merely take it away any time they want.

So unless this went though the court where the court ordered he could not sign for his self, the POA giving up that right will most likely not be valid in court.

If you can prove the bother lied and did a fraud ( before he died would have been better) you sue the brother for fraud