H1B holders in USA?

The temporary ban will only apply to those outside the USA.

I agree. Follow the instructions for answering each question.

My brother is a citizen of Ghana with a multiple entry B1/B2 visa? Can he enter the US nowadays?

Those still in possession of valid visas to the US should be admitted.

Can H4 visa be issued for H1B already in US?

i did not read a prohibition on H-4 visa issuance.

Will the new Trump H-1B ban impact visa transfer for people already in the US?

The new EO seems to only affect individuals applying for the visas in question from abroad.

How can I establish my continuous presence for AOS?

You already have an attorney in this case. All your questions should be directed to him/her.

Green card renewal and passport ?

You don't need a valid passport for applying for the renewal of your plastic GC.

Separate. Move. Apply for divorce. Apply for new I-751 with a Waiver. Hire an attorney.

Your US work experience here is not going to help you any. You have to obtain/provide your foreign experience to show meet the job offer's entry...

Can I stay in US on while F1 change of status is filed and pending. I am currently on H4 (EAD) and am about to file for divorce?

You can legally continue remaining here while your COS is pending and after it is hopefully approved.