More information is needed about your case and intent.

A review of his case must be done to better assist.

The traveler must enter with the appropriate intent not to remain.

Unfortunately you must be a USC to petition your sibling.

Explain your business in the UK and intent of short trip.

You should submit most recent year tax filing documents.

I agree with my colleague re: separate I751 for your child.

Yes you may but will need proof of divorce.

Yes you may meet eligibility requirements but best to confirm with an attorney.

Yes the Fiance visa may impact the visitor visa.