If your income has decreased, you need to file a motion to modify child support. The sooner you do it the better as your support will be modified effective the date you serve notice of your motion on you ex. While you can try to accomplish this yourself, you are much better of hiring an attorney to help you. You are fortunate that here are many good lawyers in your area. Speak to one o more and hire the one you like best.
Your ex wanting to "prove up" does not make sense. Speak to your...
Look around your mother's home for paperwork. Examine tax returns. Go to any safe deposit box. Check with banks where you know your mother banked. Speak to any known attorney or accountant your mother may have hired. Without organized records, you are on a bit of a fishing expedition. Certain investigation services will be able to locate investments for a fee;.
The situation as described, while unfortunate, will probably not be a viable cause of action. Take care of your medical problems first. Then if you still have concerns about your legal rights, bring all of your paperwork and visit an attorney who is experienced in personal injury litigation.
Your child can visit with any family members or friends you so choose when it is your parenting time. If you do not yet have an attorney, now is the time to consult with several and hire the one you like the best.