Am I wrong for not wanting my kids alone with my fiancè's father?

I like my fiancè's father. He's just really unhinged. He did 14 years in prison because my fiancè's grandfather was a sicko and nobody knew. My fiancè was molested by his grandfather and his grandfather did the same thing to other kids and when my fiancè's father found out he got into a fight with his dad and cut off his own dad's 🍆. I'm not saying I don't understand why he did it, but my fiancè's dad is just so unhinged and I'm not saying he would ever hurt my kids. He's just the type to think they're doing the right thing but end up causing trauma. Like for example, someone was staring at my fiancè's step sister when she was 12 and he felt it was sexual so he beat this person and nearly killed them in front of her which caused her trauma. He's just not all there and unhinged and he thinks he does the right thing but its still traumatizing. I just don't trust him to make good decisions alone with my kids