I think my son in law played with knives when he was ten
What do you mean?
He keeps on trying to stab me with the knives. I feel very afraid.
You should not let your children play with knives especially when they are young. If you think that he was trying to stab you, I would recommend you contact the authorities and file a restraining order. You should however try to find out first if that was really the case or you were just imagining it.
I can't do that. My daughter would not forgive me.
Are we talking about an adult? As a first step, someone needs to talk to this person about his behavior and explain that if it doesn't stop, bringing the police in is the only alternative. Meanwhile, suggest counseling.