I am the Nurse of the URI in cats... lol! Not by choice, but because I have had sooooo many foster babies with it, and it has spread like a wildfire through all of my cats. First of all, let me tell you that I have treated over 30 cats with URI, and NONE of them has died from it!!!! Even though the kittens were vaccinated, they probably had been exposed prior to their shots. A trip to the vet for an antibiotic and possible eye ointment would be best. Also, just be sure they keep eating and drinking!!! If any quit doing so, you will need to get to the vets asap for fluids! (Especially if they are running a fever and not drinking!!!)
Special foods like jar baby chicken or even can tuna (water packed) are "OK" to help them eat better. Just like us, when kitties noses are stuffed, they can't smell their food, so they don't want to eat it!
Other than that, just try not to worry .... it will runs its course and they'll be fine. As far as your other kitty.... if he is current on his shots, he should be fine! He may get a "touch" of it, but it shouldn't be nearly as bad as what the kittens will have!

Good luck and welcome to PT!