please help

What is the name of your state? mn

Hi there. My husband and I are married in our culture but we are not legally married. My husband's ex and them were also married in our culture but not legally too. They were married for almost four years. And during that time, they had two kids. A boy and a girl ages 4 and 6. My husband and I now have a two month old baby. He's been paying child support ever since he and his ex divorced(culturally divorced). His ex cheated on him and since they weren't legally married, the courts couldn't help him on that. I was wondering if we could get the child support payments to be lowered now that we have a two month old who needs things. I don't work because I still go to school for my education to get a good job. I know that my step-kids need the child support money too but they tell us that their mother don't buy them clothes and none of that stuff. Whenever they come over, they want things and we feel bad because we can't afford to get them anything. We can barely afford our baby. Also their mother has a boyfriend that my step-kids say hits them. How can we prove to the courts that he hits them? I know their mother will deny it. Also, it's just the kids telling us that he hits them. We want to do something about it but we can't because we don't know what to do. So please help answer these questions: 1.Since we aren't legally married, is there any possible way we can get the child support payments lowered? 2.How can we prove to the courts that my step-kids mom's boyfriend hits them? 3.If my step-son doesn't want to go back to his mother's house, and we don't want to force him, how can we change custody? And what are we to do?

opps sorry wrong page..