I found out that my father who lives by himself is allowing a 60 year old man who he met in the park, who is homeless to come to his house to eat and take a shower. He is also going to the grocery store to buy him food. The man states that his wife died about 6 months ago. My father told him that I would not approve of this and had to stop. The man told my father that this is his house and he can do what he wants to do. This man has had 25 criminal charges and/or convictions.
I worked with the homeless in our community (as a volunteer) and one of the things they stressed was not to give them your last name or to see them outside of their structured support environment. When they first started the program, one of the volunteers struck up a friendship with a homeless woman who started staying with the volunteer. Her boyfriend started staying as well and to make a long story short, they murdered the volunteer. It almost sank the program. That's not to say in any way that homeless people are going to murder your father, but he needs to leave their care to professionals who have the structure to offer help and to determine how to protect the volunteers. If he can't understand that, then he needs to be monitored more closely, because his cognitive skills aren't there.
I'd contact the local police department to see if one of the officers would speak to your dad about the dangers of what he's doing. Or someone from the local homeless group that offers support. Good luck and keep us posted!