I hate to be the only doom and gloom person on this thread and I know you inherited them…
I am in MA and honestly, think that if you can, you should do everything within your resources to get them somewhere safe in the winter. We are next to two old farms and they had a feral cat colony for the longest time. We did our part and tried to catch a few, one even made an excellent house cat but by and large we did the TNR program …
It’s not the cold you need to worry about in MA. It’s the predators. As it gets colder the prey gets scarcer and you’ll be finding the hawks, owls, fox & coyotes get awful close to the sheds mid-winter. We have had them come right up into our paddocks and pluck chickens off the fence - I even saw a fox a few years ago under our shed. At 7 and 10 the cats are old enough to know better than to be out at night, but as they get older they also get less sharp… so they may be on borrowed time… so if they don’t have a ‘shelter’ or hiding area where they can completely escape a predator I’d want to make one. Something like a place they can run into like a tack room or shed - not something like a Rubbermaid because a predator can easily get into that too.
Any way, not a single one of our TNR/barn cats made it through the winter. And these were cats that grew up in the area and weren’t young. The feral colony is gone now, thanks to an intrepid coyote population.
We have a fully feral barn cat now I am trying to convince to come up to the house, we have a vacancy – but he is very feral and I worry for him this winter. He is not approachable and I do worry about his longevity if he is outside.