50 F is not really dangerously low – indoors they’re obviously protected from rain, snow and wind – and they seem to be compensating well by eating a lot more hay – which is normal, healthy bunny-behaviour. How do they appear to you? I mean, are they alert, interested, are their eyes clear, fur shiny and in good condition? Rabbits get thicker fur when it starts getting cold, so if they’re gradually exposed to a lowering of the temp, (like they would be in the wild during the fall) they have time to “prepare themselves” by growing thicker, warmer fur.
If they are young (6-12 months or less) you should probably give them more pellets though, because growing animals need more protein than adult ones.
If it becomes really cold you could put hot water-bottles wrapped in fleece or towels near them, but not so they can’t move away from the heat. If they’re in cages you could put the water-bottles just outside the cages so they don’t try to eat the bottles or towels.
Be extra careful when Socks comes home after his surgery, because after surgery, bunnies are sensitive to cold. He may need a hot-water-bottle to snuggle up against then.