Yes you should be able to with proof of your custody.

Yes you may change your status to another while in the US.

You may correct this at time of interview.

Yes the return resident visa SB1 application.

Yes it is advisable that you work with an attorney prior to submission.

Please refer to the USCIS webpage direct filing address page for your specific case.

Each beneficiary requires a separate I130.

Their stay was valid if during a timely filed extension. Consult with an attorney prior to travel.

Update the I864 at the time of interview with all current employment.

Yes you may contact USCIS to withdraw.