My stepchildren are coming this weekend. how can i make sure they don't help my children run away?

they have been inciting rebellion into the hearts of some of my oldest daughters and i am afraid they will turn from us in favour of the easy, sinful lifestyle my stepchildren have with their mother. these children are evil and manipulative and disobedient to their father and myself but my husband says they must stay so i must accept it. i cannot tolerate them provoking mine into running away! they don't understand that the life they idolize of their half siblings is a life absent of Jesus and they are very attracted to it. do we put locks on the outside of their doors and separate the stepchildren?