Thank you for your suggestions! I just went out and opened the door to our crawl space and turned the light on under it. It is nice and warm under there. I left the door open enough for them to go in but not so much as to make the crawl space cold. I called for them so hopefully they heard me and will go under. They have plenty of food in their bowls for tonight. I will have to give fresh water in the morning. It will be frozen tonight.
My only problem is that cat food is expensive, even the cheap stuff. We already have three cats of our own and two dogs. Money is getting tighter and tighter but I will do my best to keep everyone fed. Our cats are all on the plump side! i just leave food out for them 24/7 in our laundry room.
Anyway, thanks for your suggestions. It's an awkward situation. I feel badly for the neighbor on the other side of these people because they have a beautiful yard. In addition to neglecting their cats, they neglect their yard. There is junk all over the place.
Oh well.