I have to strongly suggest taking these fish back to the store. I've kept discus for many years and bred discus in the past for roughly a decade. I can say with almost complete certainty that these fish are not going to survive and certainly are not going to achieve anything close to their potential in size and vibrancy.
Juvenile discus are handedly the most difficult freshwater fish to raise properly I've ever seen. If you cannot perform daily water changes upwards of 50% of the tank's total volume, and feed 4 - 5 times per day, you'll end up with unhealthy fish if they do survive to maturity and those that do will more than likely be permanently stunted. For any community tank, the only discus worth consideration are 5"+ full grown fish.
Secondly, even adults require substantially higher quality water than most fish keepers will ever come close to providing. I recommend no less than 50% water change per week. The water change volume is completely dependent on the stocking and observing the fish, I've seen heavily stocked community tanks requiring 50% every 2 days...
The crux with both juviniles and adults is the water needs to be seasoned, basically it needs to sit for 24 - 48 hours before being added to the tank so that the chemistry can stabilize and the keeper can ensure that Chlorine and Chloramines are properly removed, you must use a chlorine treatment for this or use reconstituted RO water. For juveniles this typically requires hours of work per day just in preparing water. Many professional breeders I've visited, change 100% - 200% of their tank water per day until their discus reach 5 - 6in.
Finally, discus are a community fish and should be kept in odd numbers with no less than 5 fish unless you have an established pair or a humongous tank, like 300 gallons or more. This is to minimize and distribute aggression between fish, they're cichlids so they're an inherently aggressive fish, and without enough fish to spread around aggression, you'll typically end up with a single fish without a large enough number to prevent the smallest from getting bullied.
So what you have right now is a situation where it's unlikely even an experienced keeper could get your fish to thrive. The tank is too small for a school of discus, bare minimum for an established pair, personally I would suggest 90 gallons is the absolute minimum I'd even consider for a small school of fish, and even with a 90 gallon tank, you're going to need to perform roughly 50 - 70% of the water per week for 5 discus and very few other tankmates.
Anyway, I hate to give advice like this, but I've just seen it too many times and seen too many fish stunted or outright not survive. Unless you're prepared to establish a fish only tank and feed and water change like you've never imagined or setup a large tank, both of these require a lot of work since you don't have a cycled tank ready to go, it's really unlikely you'll get good results with these fish. When they are stressed they are highly prone to diseases, stunting, and just not surviving.