This is between you and Dad, not you and your son. IF you and Dad agree that this is the right thing to do, the son cannot veto your decision.
You should work with an attorney to draw up the proper papers and get this done . . . quickly.
I hope you're not saying that your trying to discharge your divorce lawyer's fees in bankruptcy court and wan the divorce layer to continue to represent you in the divorce case.
Why is she seeking to withdraw? Just remedy the problem. I suspect she is withdrawing because you owe her money, right? If so, pay her and she'll almost certainly stay with you. You can't expect her to work without getting paid.
So, what's the problem between you two?
This will probably be teh very first question to be answered by the attorney you meet with to prepare your will(s). If you don't want ot pay an attorney, and intend to prepare your will(s) yourselves using an online service, you can try asking them for advice, but I know of only one such service that employs attorneys to answer legal questions free-of-charge.
You're probably better off meeting with an attorney face-to-face.
Bigamy is a crime in IL (I assume your father is in Illinois). Your mother would have a cause of action for support both for herself and the children.
A few questions: 1) when did all this happen, and 2) are there resources available to afford the litigation?
You should probably stop taking legal advice from your spouse and family. Hire a lawyer and get some real legal advice.
You don't give enough information to allow an attorney to answer your question about whether you'll have to pay maintenance.
Below are some legal articles that may help answer some of your questions, but CALL A LAWYER.
Some "uncontested" cases costs a few hundred dollars; others cost several thousand dollars -- it depends on the size of the estate, the complexity of the agreement, and where things stand in negotiations. To most couples, "uncontested" means they don't fight anything out in court. They might fight and argue and haggle over a lot of things (like, for instance, how much child support one should pay to the other, or who gets the nicer car) but, as long as they never have to take the witness...
I don't know what a "Thai Prenup" is, so I may not be giving you a fully-informed answer.
Assuming, eventually, the prenup possibly would be enforced or contested in an American court, then it would probably be best to have it crafted under American laws. If you anticipate the agreement may eventually be needed in the Thai legal system, then it should probably be crafted with an eye toward those laws and norms.
Prenups from other lands usually are valid and enforceable in the U.S. -- so...