The petitioner can withdraw their petition. Plus he would need to submit additional paperwork once the priority date is current as well.

There is a waiver for the K1 requirement that you have met before. You can try that. But he will need a passport.

I do not see anything about it being free. You could apply for a fee waiver. https://www.uscis.gov/i-912

The best advice I give people is the amount of time spent in the US, you should spend out of the US, before coming back.

The receipt should come soon. 2.5 years is a long time for a case to be processing.

H4 visa holders can only obtain an EAD if their spouses I-140 was approved....

Probably not worth the money / effort. Are you processing through the consulate? If so you do not need the notice. If you are adjusting, you do not...

USCIS does not investigate anything. If police were not involved then it is not relevant to the case and will have no effect on anything. He's good...

Yes you should file a bridge b2 extension. A COS to J2 should not be an issue.

The initial interview process taking forever is unfortunately standard. The USCIS offices are slow and were additionally delayed because of Covid....