Filling out child support modification papers

I dont know what to put for income taxes, she lives with her parents and husband what do I put for their income, She also lives rent free but has always claims that she pays rent. How do I prove it? She also has 4 degrees in social work but now states she is self employed what do I put for her income? Since I do not have medical with my employer her new husband has my son on his medical. Since he is paying it through his employer can she claim that she pays it? I am having a hard time with these areas, any help would be appreciated!