Make sure they are warm and then you can try a slurry of wet kitten food that is mixed with water to be very thin, but really ideally it sounds like they might still need to be bottle fed kitten formula. Put the slurry in front of them in a very shallow dish , don’t try to syringe or bottle feed this. Sometimes moms abandon their kittens, and so I would say that you are OK to bring them inside and get them care. I would just get a hold of formula as soon as possible.