Sexual threats to other, kicking others in the genital regions and wetting the bed are signs of sexual abuse/molestation. Is there a possibility that the mother or her boyfriend has done anything to him? I agree with AnnieBrooke and CaBarajas. He needs counseling.
Is this boy your biological son? Are any of the others yours? It is not clear what the relationships are..
Sorry...I meant, try as hard as you can to GET through to his dad.
My stepbrother did some of the things you describe above. Not the sexual remarks/threats, but some of the other things. Our parents (one real parent and one stepparent) knew there was a problem, but did not seek help for him and became offended when teachers or other authority figures would suggest counseling. Things did not end well for my stepbrother. Try as hard as you can to through to his dad, for the safety of everybody around him. I agree with AnnieBrooke...talk to the grandparents. Maybe they will help your ex to see that this boy needs counseling.
Yes, he needs some counseling. I have a nephew who is going through almost the same thing. He is 8, he is my brother's stepson, the dad has custody due to that the little boy lied to the his dad and told him that my brother bit him up. He had bruised but was from playing outside and falling off the swing set. His dad filed charges on my brother and so I think that is where things started going down hill. My nephew knew that he had the power to do anything he wanted and all he had to do is call his dad. When he comes visits with his brother's and sisters my brother's kids he is always picking on his little brother and telling him to do gross things like lick the table or hit people in the private parts. He also lies all the time and blames his little sister for everything. I think he is gotten worst because his dad does not want him on medication and does not think he needs counseling. It is hard to reason with a parent who has custody but at the same time does not even spend time with the boy to see what is actually going on. I really do think though counseling would be the best treatment.
Talk to the grandparents, see if the child is getting any counseling. I'm concerned for the 4-year-old in this situation, but things might get better as they are away from their abusive mother. I would not expect you are going to have your baby around this kid by himself, but I do feel for his little brother.
Just remenebered he also told my son his girlfriend kissed him on the lips. He told his dad he broke up with her cause of it. But didn't say that to my son. He is also obsessed with hunting n killing things. Doesn't matter what it is he wants to shoot it. This kid freaks me out. Noone seems to be concerned and he has a 4 year old brother who models everything he does. He's sneaky. He will say mean things quietly to my son to upset him when he isn't getting what he wants. But quiet so he ownt get caught. The kid scares me. And I'm worried to have my new daughter around him.
His dad also told me he has been wetting the bed recently. Mom just lost custody of kids a few months ago for domestic violence against kids and with boyfriend in front of kids...and generally being a loose cannon. and he is at dads full time now and grandparents watch him too. So there is some adjustments going on with living situation.