Have you tried this yet? This saved us (or at least our sleep) this winter with all the head colds the kids had. (It apparently works on the flu as well but we were lucky enough to avoid having to test that theory – knock on wood!)
Simply cut an onion into small chunks and put it in a dish as close to your kids’ head while they sleep. (If you start to tear-up when you enter their room, it’s working.) The kids are a boggle of gross when they wake up, but at least they were able to breathe and sleep through the night. You can also make a poultice if y’like but I didn’t try it.