How safe are these cats from the elements in this scenario?

Five cats in a corner off the garage floor some three feet with the door close in the Midwest in a large felt "pet bed" and the lights off. Should they be in the basement?

Depends how cold it is. If it is cold I would put them in the basement. I do not know how cold of temp a domestic cat can take, but I think they would be happier if they were not cold.

If the basement is warmer, move them there.If you keep them in the garage you could make some beds for them from deep plastic tubs or cardboard boxes and fill them with straw. It's great insulating material and they can snuggle into it to keep warm. This article on building winter shelters for cats has lots of information and advice you might find helpful.http://www.neighborhoodcats.org/HOW_TO_FERAL_CAT_WINTER_SHELTER