You may file for all three and then determine if your parents should do so at later time once they become LPRs.

Yes this is possible but more information is needed about your marriage and history. Consult with an attorney for guidance.

Your question is unclear. Best to wait for mailing from USCIS.

It is not advisable to drop off documents to USCIS without being requested to do so.

You may indicate that yes someone has filed on your behalf.

You may reschedule the oath ceremony without issue.

It is not advisable to return to the country from which you claimed asylum.

No, not unless the priority date is current.

Yes best to apply for an extension under these circumstances.

Best to contact USCIS directly to inquire.