My man's family needs to back off and stop disrespecting me, how am I wrong for using him for his money?

I don't think what your doing is wrong especially because he is obviously using you too. If you do want to stay in his house though then you'd better bite your tongue when it comes to his family because he could throw you out in a second. Also, while you are there I'd consider saving up money because what happens if he decided he doesn't want you and then you are left with no money and no house or job. Honestly just do what makes you happy but be safe and try to have a back up plan.