Have three cats with this problem have taken them to the vet and they get a shot and some pills, over time they do better and it is nice to see them getting batter and more active. Unfortunately I am also feeling terrible and hope it is not because we are both sharing the same bug.

Go to the vet, get the antibiotics and give them to the cats. Saved a few cats in my life this way.

Cats from a shelter almost always have an upper respiratory problem. Don't know if yours are from a shelter. Cats won't eat if they can't smell their food. I've found that meat based baby food will often "jump start" a lagging appetite. Of course that's not a long term food for them. Vet first is the best.

Definitely need antibiotics. I was a vet tech over 20 years. They'll start to improve pretty quickly after they start medication.
Good Luck!!

Veterinarian.

Vet. Mine did that & they have a good remedy for it.

The vet is best. In the meantime, you can bathe their eyes gently with a warm, damp cloth. Also, if possible, keep the air moist to help them breathe. Shelter them from cold and damp so they don't catch a chill while making certain they don't overheat.

Best thing is to the vet.

Possibly sprinkle L-Lysine on their food to boost the immune system. Ask the Vet first though. I'm not sure if that's okay to do at their age.

It's very much like a cold in humans. It passes in a week or two or the vet can help it go faster.

Vet is your best option. They likely need medication if it’s to the point of having goop around their eyes/nose. Just make sure they get plenty of fluids