This is most likely stress since you've had them a few days only, and have a smaller than recommended group. Try and increase the amount of movement around the tank, add another couple more fish and give them a month or so to settle. A healthy Discus will go over a month without food, so a few days without eating isn't enough to cause immediate concern
Are you sure Ammonia, Nitrite and Nitrate are all zero? If so, what filter media do you have? A cycled tank should always have a Nitrite reading... What test kit do you use (make and type) and how old is it?
Stress Coat works by irritating the fish to increase the slime coat (or at least I assume this to be the case as I can't get a strait answer off the API rep at work, and Aloe Vera [one of it's components] is a well known irritant to fish). If this is your water conditioner and you intend to keep the Discus long-term, Id chuck the bottle and get the same brands usual plain water conditioner
Discus will require 4 feeds a day as juvis, three a day as adults, with at least 1/2 the diet as fresh or frozen food. They may take flake, but it is unusual, so your dried food should be something more like a Discus pellet food like Tetra Prima, or Vipakraft Discusin.

You should try an have at least 5 frozen food to choose from and three fresh like peas, courgette and a live feed, that you offer at separate times

The most important thing about Discus diet is that it is varied. If it is all one food they will often develop HITH (Hole In The Head) disease, a dietary related illness
BTW, you'd likely get more relevant responses if you stuck to one thread if your further issues are developing after some initial ones. If the issues are linked, it allows the posters to spot the link more easily if the recent history is all in one thread
For the moment, keep a close eye on them. If there is any excess slime, loss of colour, flicking/rubbing, visible parasites attached to them or any gill clamping going on, get back to us as the symptoms could be a few disease issues, but with new stock the issues are almost definitely stress related.
Where are you based, and have you got these fish direct from Germany, or via a shop?
All the best
Rabbut