No this is not advisable for petitioner to act as translator.

This shouldn’t impact a good faith I485.

You may request a National Interest exemption.

The I485 must be approved in order for GC to be processed which will take 8-13 months after vawa approval.

The international marriage certificate should suffice.

This is unfortunately common. Contact USCIS again before proceeding further.

Yes the 90 day rule applies to immediate relatives.

Yes a second extension may be requested.

Yes indicate your stepchildren on Part 5.

Yes you may make an expedite request but he may or may not be approved.