Did you recently add any wet items like fish, snail, crab, coral, live rock or the like?
From the breathing issues and because they are clownfish I would suspect a Brooklynella hostilis infection. If it is Broolynella you may also see some whitish plaque on the fish.
With Brooklynella there is not much time to waste. I would immediately prepare a hospital tank (HT), 10 gallon with a heater and a HOB filter should be enough.
Before you place the fish into the HT give them a 10 to 15 minute freshwater bath followed by a 30 to 60 minute bath in saltwater with dosed with formalin/malachite green (Rid Ich Plus). Aerate this bath well since formalin binds oxygen! These baths will give the fish some relieve buy reducing the infection. To clean them up completely they need at least a month of treatment with some medication.
In the HT you can either treat the fish with malachite green alone (Rid Ich) or try chloroquine phosphate (Ich Shield).
The other disease they could have is Amyloodinium (also called velvet) - in that case I would go the Ich Shield route
