Going to a judge is an option, but probably not necessary. It sounds like your divorce decree spells out the extent of his ownership interest in the house. I suggest you figure out how much his value in the house is and then figure out a way to buy his interest from him (or if he owes you back child support or other debts figure out a fair swap of some kind as you suggest). A real estate attorney could assist you draw up the necessary paperwork whereby he can transfer his share of the ownership in the house to you. Then you file that paper work, usually with a county auditor or recorder. Of course you're going to have to track him down so he can participate in this process.
As for the mortgage on the home, that's probably a different story. You'll have to review your mortgage paperwork and work with your lender to determine whether he can be removed from the mortgage. A lot of times a lender won't remove a co-debter because they want to be able to go after both of you if one of you defaults on the mortgage. You could of course try and re-fiance and as part of the process update who is on the loan paperwork. I hope that helps.
Providing this general response does not create an attorney client relationship.
Although I do not practice in your state, I agree that you must have your ex's cooperation to be able to work this out without and have real estate documetns signed without having to go back to court. If you do locate him and he refuses to cooperate, you would most likely have to serve your ex with the court papers, whether he decided to oppose or even participate or not.
I believe that you will need to speak to an attorney to get the resolution that would best benefit you and your child. Good luck!
This is not intended to be legal advice or create an attorney-client relationship. If more information is needed, you should consult with an attorney in your state regarding the specifics of your situation and the options available to you.