My boyfriend and I recently decided to cohabitate.   I have a 10 year old boy and a 6 year old boy. I have full custody, and they visit their father every other weekend.    He has a 2 year old girl, a 6 year old boy, and an 8 year old boy. He only has them every other weekend.   We have all 5 children every other weekend. It has turned into a real nightmare. The 6 year olds do nothing but fight. I am the only one who disciplines, and am constantly the bad...