Put all this behind you and decide what you want to do from now on.
If you want to keep Discus:
Firstly consider they are not beginners fish, they are not as hard as some sites/books make out, but they are unforgiving of mistakes...
For a group of 5-6 Discus you'll need a 4 ft tank, around 48x15x18 is probably the minimum size, bigger is better though of course. For this to work out you need to leave out the sharks and the loaches, I'd take them back to the LFS. You'd have some room for some Cories/Tetras and other small fish that would live in the water parameters of Discus.
To keep Discus your basically keeping water and a clean tank. They need soft water that is soft-neutral, so you'll need to test your tap water for pH and hardness. Try to match the parameters of the place you purchase your fish from, and I'd recomend finding a Discus breeder as some Discus in normal LFS can be fairly low quality.
In order to match the water parameters you may need to soften your water, this is best done by using RO water. This is basically water with 0 hardness, it can be mixed in with your tap water to achieve the required hardness or chemicals such as Kent RO right can added to it as RO water cannot support life on its own.
You can either buy your own RO unit or buy RO water from an LFS. It works out cheaper over time to buy your own unit. So you'll need to space to store/mix the water your producing for you water changes.
If you buy baby Discus your better off keeping a bare bottom tank as they require very very clean water. I would suggest you buy adult Discus as they are far more forgiving.
So when you get the 4ft tank you need to set that up alongside your current tank, I'd have an external filter for the 4ft and run it on the smaller tank for a month or so to cycle it. Then you can transfer it to the 4ft and add some fish, but not the Discus, add the other tank mates such as Tetras/Cories to slowly build up the load on the tank, the Discus should be the final addition and if you can add them at the same time so they can all settle in and then fight for territory at the same time.
Hope that hasn't put you off, if it has I'd say tank all your fish back to the LFS and buy something that will happily for life in your smaller tank. Oh, and remember, don't trust any LFS, no matter how good their advice it can't hurt to double check it yourself.