I need to get access to my deceased mother medical records because I suspect that my sister obtained my mothers signiture while she had alhiemers dis

What can I do about my sister. There are four siblings that were suppose to share the house that my mother left when she died. One of my sisters, I suspect had my mother who had alheimers disease at the time and eventually died of, transfer the house deed only to my sisters name without telling the rest of us. Ten years later, we just found this out. Now she refuses to share the rent proceeds from my mothers house. I have been told that I need to get my mothers medical records to prove that my mother was not capable of sighning any documents, please help, thank you. Sincerely Marcus Morellon.