Two H1 Transfer approved simultaneously,

[su_resh55]

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.