No this is not possible after GC has been issued.

Best to inquire directly with USCIS.

Yes you may remain while the case is pending if application was timely filed.

No not based on the information provided. You must wait 3 years after being married to USC and being LPR.

It can take up to 120 days for decision.

Yes you may do so but sibling petitions take many years.

No this should not impact your immigration status.

Best to review the form instructions on USCIS webpage. Good luck!

Provide the documentation at time of interview.

That alone should not result in a denial. Consult with an attorney for assistance.