KMR (kitten replacement milk) is what you'll need to feed them for at least a few weeks. I know there are different brands out there. You can get either ready-to-feed or powdered. You can get it a pet store or places like Walmart or Target.
A cat's normal body temperature is about 101 degrees. So if the kittens were cuddled up with mom they would be quite a bit warmer than room temperature. You don't have to keep your whole house that warm. You can put a heating pad in the bottom of the nest, covered with a towel or blanket, on the lowest setting. That is not the safest option because of the electric wire, and also because not all heating pads will have a low enough setting.
A better solution is to take an old sock, fill it with uncooked rice, and heat it in the microwave. Try it for just 30 seconds or a minute first. If you have a thermometer you can check the actual temperature of the sock. If not, just have it so it feels warm to touch, but not hot. You don't want to burn the babies. The sock(s) can be shaped to fit around the kittens so they can cuddle up like they would with mom.
Bless you for taking in these babies.
that they will thrive with your care.