As for lasting over 2 minutes, particularly given how tight their cunts are bound to be, you're probably looking at half a bottle of whisky + a Viagra. Then you might be able to keep it going until the one you're fucking licks the other to orgasm. Still touch & go, probably....
So you're gagging to fuck both, but once you're inside one or the other, is there ANY chance you're pulling out before you've shot your load? Pretty much impossible i'd say. Best to fuck her doggy while she licks the other one out. Then at least you can stare into the cumming face of one while you're spunking hard in the other.