Can I install two independent gfci outlets in one double-gang box?
Take the incoming hot (black) and wirenut it to black pigtails going to the brass LINE HOT screws on each GFCI.  Take the incoming neutral (white) and wirenut it to white pigtails going to the silver LINE NEUTRAL screws on each GFCI.  Take all the grounds and wirenut them to each other and to bare pigtails to the green ground screws on each GFCI -- if you're in metal conduit with metal boxes, simply get self-grounding GFCIs instead.

With a single 12-2 and two yokes, you'll be nowhere near box fill for a double gang box, by the way.