I’m with the let them roam crowd. Get an old cooler big enough for all of them and cut a hole in the lid and put it on its side. It will keep them warm on the back porch. They will be fine, and no more litter box too.
Please do not do that. I cared for a feral stray in my neighborhood for 9 years. She had a secure location to live in my walled-in outdoor patio with a warm box, a filtered water fountain, and an automatic feeder. She was a very sweet cat who made it very clear she did not wish to live indoors. However, the last year of her life was pure hell. The feral colony nearby had picked her out as old and fragile. (She still had her claws, but had lost all of her fangs, mostly through cat fights, where she had formerly ruled the neighborhood.) She was coming home injured more and more often, and some of them were pretty bad. It eventually got to the point where she became afraid to leave the patio, but that didn’t stop the neighboring challengers from coming onto the patio after her. After one of them bit clear through her paw and broke it, I finally had to make the decision to have her humanely euthanized. If this was the end for a street smart cat, imagine what will happen to these older, pampered kitties turned out into the street. Not to mention what a nuisance that would be for the neighbors.