I would try and return all of them, to be honest. A good LFS would take them back, maybe even just for store credit. I would then do a fishless cycle, and read up/find some acceptable inhabitants for a 5 gal tank. There are many many possibilities for fish and inverts that are acceptable for this size tank. Unfortunately many of them aren't commonly available at run-of-the-mill pet stores.
The bacteria-in-a-bottle products like the FilterStart are hit or miss... sometimes they work, but often they don't... it just depends on how the product was stored, and how old it is. I personally avoid adding anything to my tanks accept dechlorinator during a water change, and some fertilizers for my plants... the rest of the chemical additives do little to actually fix underlying issues/causes of problems, like putting a band aid on a bullet wound, so to speak.