Can i put these fresh water fish together?

No, the cray fish will most likely eat your other fish. Puffers are pretty aggressive. Black ghost knife fish could kill your mollies and sword tails if they are too small. Discus are really delicate and require precise conditions, but mollies like brackish water. Keeping any of these fish would require at least a 30 gallon tank, keeping multiples probably around 60+ gallons. If you are new to fish keeping start with something easier, if not, pick your favorite and choose tank mates based around it.