You can set up a light which puts off a good bit of heat or a heat lamp in a cozy corner for them to cuddle up in. Just be careful it's not in contact with anything that could catch on fire.

You could try hay... or get a couple of those huge dog beds and put them down. If possible try to keep them off the ground because it gets a lot colder a lot quicker there. I take in strays all the time but I can't always keep them in the house. I put down a layer of cardboard boxes then line it with heavy, down filled pillows. Hope this is helpful.

There are cat houses available that are small enough to keep out dogs but large enough for 2 cats to keep warm. Outdoor Pet Structures sells them at www.outdoorpetstructures.com. You don't need anything else.