OK I understand the situation a little better now. So he is sort of your dad's carer then? That seems to be a pretty common story - you trust someone to care for a family member and then they take advantage of the whole family. That's awful. I can understand not wanting to do anything much about it until your dad is unaware - that might make him just really mad at you. Maybe if you just keep letting this guy know you are watching, he will stop it.