It is more difficult do collect spousal support than child support. You can request it but courts are typically less enthusiastic about garnishing for spousal support than for child support.
He obviously is not onboard with the deal you struck. Holding things in limbo through expensive appeals and legal motions is an effective strategy in our legal system. The personal property paid for by the minor nephew is not a black-and-white issue. The appeal and your efforts to enforce the deal sounds like it will be a long expensive road.
You have two choices: talk to him directly and find out what he wants and make a settlement that gives you less than you want but short circuits all of this. Or get a good lawyer on retainer and stay on top of it and apply as much pressure as you can to see the original agreement through. Neither will feel satisfying to you.