future step son hitting me

I am currently living with my fiance who is recently divorced with 5 kids. Our kids go to school together with no problems between them. The ex wife keeps telling them I broke them up which isn't the truth and my fiance talking to them doesn't help. We to took them to Chucky Cheese for one of their birthdays and the 13 year old son hit me with a hot pepper glass holderr in the head. It really hurt and they were calling the cops to have him removed but my fiance took him outside and home. I pretended it didn't hurt. His ex's brother came to our house with a knife and shoved it in my fiance's stomach and I called the police as he threatened to kill me and my kids if I called the police...our case is waiting to be heard. Now at school I had to do lunch duty and the son shoved the door into my head and body. Another mom saw it and I asked her not to report him to the principal. He says he will kill his dad and me some day. Now mom at school tried to hit my car in front of the principal with her big truck. If a child hit you do you have the right to defend yourself? Mom buys him a present when he does these things as we have it on video tape. She gives him the high figh and says kill the 'B....'. He is very violent as is the mother and I worry about my safety and my childrens.
My fiance has stopped picking them up because of the violence and they won't come for christmas unless he moves home with their mom, It has been 2 years and i don't think it will ever get any better. he is a great dad but mom wants to ruin his relationship with them. please help.

When going through a divorce, it is best to be very considerate and respectful for the needs of the old family. It may be prudent to delay moving in with a new partner until the old family members have calmed down and got adapted their new roles.

It is always best to try to find solutions which everyone is satisfied with, so that children who feel abandoned will not get so desperately unhappy.

Mixing together the old and the new family may not work. Sometimes it is better that the man meets with his children and his new partner at separate times.