Only after the child reaches 21 years of age.

Contact USCIS directly to inquire about the many reschedulings.

Yes that is okay as long as you can return if biometrics are scheduled.

Yes that should not present an issue.

You should apply for a travel document prior to travel.

Yes the K1 is acceptable form of proof.

You would indicate married until the divorce is final.

You should depart prior to the validity period on the I94.

More information is needed about your case to properly assist.

Best to work with them rather than sue them.