They are natives It was just recently cycled with the chemical that removes chlorineThey're dying because your tank is far too small, probably not cycled, and incredibly over-crowded. As I've said, you need to research basic aquarium care and obtain only fish that are suitable for your tank. About the only fish suitable for a 5g are guppies, endlers, microrasboras, or a single betta. The tank has to be cycled, it has to be heated for non-natives, and the water has to be treated.
When deeda asked for water test results, they didn't mean what the water looks and smells like. You need to get a test kit and figure out exactly how much ammonia, nitrites, and nitrates are present. Also, do NOT add more fish or they will die painfully like this batch.
okayThe chemical you added is a dechlorinator. It does NOT cycle an aquarium.
Fish produce ammonia. Ammonia is toxic. A cycled aquarium is an aquarium that has built up a series of bacteria that turn ammonia into less toxic substances. You need to test your water for ammonia, nitrites, and nitrates, in order to find out if your aquarium is cycled. You cannot cycle your aquarium by changing the water or adding water conditioner.
It doesn't matter that those fish are natives, they still can't stand being in an un-cycled aquarium. They're being poisoned, which is why they're dying. Also, they're all either too active or will grow too big to be kept in a 5 gallon.