My life is so hard

My kids fight really bad. It starts as soon as they wake up. It can be really bad. I have three boys and they all have and still hit their sister really bad but she also hits them and is not afraid of them and she is the youngest. The boys beat up each other too. They all really fight. It's so hard on me. I'm re-married and their real father who they live with 50% of the time with is a real mean man to me and my new husband. My ex-husband called my new husbands work and tried to have John fired and my ex-husband doesn't pay child support and he also owe's me thousands of dollar's of back child support. He put everything in his mom's name so that it shows that he has no money. He is not the greatest co-parent to work with. He encourages my kids to be mean to me and be bad at my house. It's so hard. I used to have them all in Martial Arts so that they could learn self-control but I can no longer afford to have all four of them in it. What can I do to controll my kids from beating each other.