Stamping for two approved H1Bs

[dithr]

Hi

I have two approved H1B petitions for company A and B and have to go for visa stamping.
company A is the software consulting company where I am currently working and company B is an US product company.
Due to some personal problems I prefer to go for stamping for company A. But I have below questions

1) If stamping for A gets rejected/Admin processing, can I go for stamping company B petition?

2) If my company A visa got stamped without any issues can I travel for company A and switch to company B after reaching US?

quick response appreciated.

Thanks