I was working for company A in H1B visa and went to my home country for visa interview. The consulate kept my visa request pending and issued form 221g. Since I have a valid H4 visa, I returned to US in H4 Visa.

I already have an offer from company B and they are ready to do my H4 to H1 change of status. My current employer also wants to do H4 to H1 conversion. Here are my questions, can both company A and B apply for my Change of Status from H4 to H1?
If both are approved, can I choose the company A or B to work with?
Are there any legal issues involved in it?