You are eligible for 60 days grace period provided I-94 is valid. A new employer can petition and a change of employer can be filed in a timely...

If AOS was timely applied within authorized period of stay, then you are permitted to stay until a decision is made on your application.

If your criminal attorney has not advised you consult with an immigration attorney before accepting any pleas then his is failing his duty of...

He can reapply however best to have an attorney review the past arrests or charges to ensure they will not be pursued.

can I use this approved NIW (approved few years ago) to file for adjustment of status to a Green Card when I move back? Yes

Can she only apply for naturalization while I delay it or I have to apply with her since I am the primary beneficiary. Yes

(1) Can I switch job to a new employer in same or similar job under AC 21 , even though new employer is not at all related to my current employer...

To work, your friend will need work status. Depending on his caliber, skill set required for the job, there could be numerous options.

Yes, you will apply as derivative if the same priority date is current for your category. If not, you will not be able to file

If COS was applied and approved, it will override the previous issued I-94 given on entry. You are expected to maintain the last approved status.