Me and three others are playing Minecraft. I have Xbox Live Gold. Three more players on the same console don't.
Is it possible to play an online game (with another console of mine), when only one player has Xbox Live Gold?
I do believe this is possible. If you sign in with the account that has gold on "xbox B" and set it as your home xbox, then actually play with the gold account on "xbox A", everybody should be able to play together over xbox live with one the one gold account.
In the following link, which provides more info about gold sharing on the Xbox One, consider your home xbox to be "xbox B" in this case, and the friend's xbox on the page to be "xbox A".