Help

My husband and I have been married for 10 years. Through which he has been verbally abusive to me and my oldest son (who isnt his biological son). My question is this: I want to leave the home with both of my children. He refuses to let me go with my youngest but doesnt care if I take my oldest son. If I leave now and file divorce papers requesting custody of both children, will he have me on abandonment of my youngest son? I truly feel that my youngest son needs to have his father in his life, but the best situation for him is to be with me and his brother. Please help…