How much is too much?

So my sons father is really not in his life, he asks to visit once a month and that only to please his mother. He doesn’t hold him doesn’t touch him he just comes and takes pictures and leaves. He’s never fed him never changed a diaper and also doesn’t give me money. I would NEVER allow my son to be around him alone he just overdosed on drugs the past summer and I’m sure is still doing them. His mom on the other hand is constantly wanting to come over now, she’s also not a great person they are very grimy sneaky people. How often is too often for her to be visiting? Also when she comes she sits around all day taking pictures and it just makes me very uncomfortable.