My sick sister had her friend go to the bank and write/sign a check. The bank cashed it. Is this legal?

My sister had two bank accts but was so sick so her friend went to the bank with a check from the bank in FL and went to a MA bank and wrote and signed and endorsed the check. The bank cashed it. The problem is the funds taken from Florida bank went to a Mass bank that a family member got my sister to put her name on. 2 weeks later my sister died and the family member gets to keep all the money and that family member is friends with the person who went to the bank with the check. I smell scam but the bank said there is no harm and yet that is because the person who brought and signed the check used to work there and has friends. I called the bank president they won't do anything, any suggestions?