Hi. Few questions regarding the G4 visa holder residing in the US:

1. I know the G4 can't start a business in the US but can he sell on-line digital products he created (a computer application, a book) considering the clients are international? Or this is considered business activity inside the US and therefore prohibited?
2. Can he get a Green Card in a legal way like a marriage to a US citizen or a DV lottery? If yes, can he keep his job at the international organization if he changes his status?
3. Can a G4 dependent visa holder open business in the US? If yes, is he required to pay the US taxes?

Thank you.