Overturning a signed MSA is usually very difficult to do, but not impossible. You will likely need to prove fraud or misrepresentation on the part of your ex, or mutual mistake. I would kindly but strongly recommend you ASAP consult with at least 2 or 3 local-area Family Law Lawyers, to assess your chances at overturning the signed MSA. Considering the facts you have presented, under the Michigan Child Support Formula, your ex likely should have been "imputed" with income when calculating child support. Also, if his rich Grand Father pays all his bills, that can be taken into consideration when assessing the Parties' respective child support obligations. I wish you all the best of luck.
Answered on Jun 14th, 2013 at 11:43 AM