A civil contract would NOT be enforceable by the divorce court or by filing a contempt action.
It would be enforceable by filing a civil suit requesting specific performance. But she cannot force a bank to give him a loan -- or his parents a loan.
If OP doubted that her ex would be able to refi then
she should have asked for an order that the house be sold immediately and no reasonable offer be refused -- if it was a short sale they each should have split the deficiency.
If with profit, they each could have split the equity. She didnt' do that. Somehow she decided it was better to bring his parents into this.
Though I am confused -- if she divorced him why is SHE using the name John Milner on here? Because if this was not a divorce situation and this was a same-sex situation things would be different.