Two H1 Transfer approved simultaneously

Hi All,I work for company A and i have filled for 2 H-1 transfer simultaneously to both company B and company C and both got approved after RFE. I am still working for company A. Company B’s H-1 transfer got approved first and followed by company C’s H-1 transfer got approved. I have decided to join company C for which i have for following 2 queries?1. Is it legal to join company B even though company A’s H-1 got approved first ? 2. Should i need to inform company C before joining them about already approved company B’s H-1 transfer ?Thanks.