Yes she can request a change of location.

You can request a change of interview location.

It doesn’t appear you would have derived citizenship based on information provided.

You can send him an invitation and he can apply for a tourist visa on his own.

Yes you may but you need proof of citizenship.

It likely means that next steps are adjudication of case.

You should be allowed entry but CBP ultimately has discretion.

Contact NVC with I130 receipt notice.

Yes this unfortunately happens and you should continue follow up with USCIS.

No this should not negatively impact your case but more info is needed.