How can we find who is his POA?

My grandpa lives with my aunt. His health is pretty bad. He was in the hospital for a week then went to a rehab center and was just back in the hospital for 11 days. He is now back in the rehab center. He wants to be home but would need 24/7 care which a few members besides myself do not think my aunt can or will do even though she says she will. She can't take care of herself right so how can she take care of a 84 year old. We were told my mom is his health POA but my aunt won't let us see any papers. My grandpa should not go home at this time cuz of on going health issues.