Uncomfortable People

Denise
So my mom got a boyfriend, now this guy makes me feel uncomfortable - the kind that you can't leave your children with feeling. He got it into his head that his their grandpa, I was never asked if I'm comfortable with them teaching that to my children so I'm always saying he not your grandpa. He also takes photos of my children (nothing bad or rude) posts them on his social media... These things make me feel uncomfortable. To top the cake- he threaten my partner that he would call the cops of him, throw him in jail. That he could make anything he wanted up cause he white and the cops always believe white people. (I'm not racism or anything. All are equal) these are my mom boyfriend words to my partner. 
I don't know how to tell my mom or him, mostly him without hurting my mom.