It depends on what the GAL wrongfully did in your case, and the harm the actions caused.

The facts and pleadings would need to be carefully analyzed. Consult with experienced attorneys in the state where this occurred.

Possibly. Consult with experienced landlord-tenant attorneys in the state where this occurred.

Consult with attorneys in the state where this occurred. Many cities or counties have legal aid or other organizations that provide pro bono...

No you do not. The ex can file a motion challenging service and only then might you be required to disclose details.

Look into a motion to set aside the judgment for failure to lawfully serve the lawsuit.

If the hearing is unsuccessful, the opposing side could not withdraw the motion so you could then proceed to file your motion. These questions in...

There are too many factors to give an accurate answer. Consult with experienced attorneys in the state where this occurred.

I do not think a motion to set aside is the proper motion. It may be a motion to reopen the case. The reference librarians at the local law...

That would be unlikely to be valid but it is too risky to ignore.