yeah i would take them all back to the store and do a fishless cycle.
however it is perfectly possible to cycle with fish without loosing any, but it does require a lot of work. you actually need a half decent amount of fish in to start the cycle, do it with too few fish and they won't generate enough ammonia to get the bacteria going, i think you need 25-30% of your final stocking in to cycle the tank. you need to test the water every day, any day that you get a reading for ammonia or nitrite do a 20% water change, don't clean the filter at all, feed sparingly every other day, and yes using ammolock can help. It converts the ammonia to something else less harmfull to fish but that can still be used by the bacteria to feed off.