I would certainly say yeah, over loaded tank. Those fish are pretty big, also you should not have gone out and bought all those fish and not known even how to test water, one of the most important things you can deal with! I trust you know how to test salinity, but to test pH, nitrates and nitrites, you will need a test kit, witch you can find at your Local fish store. Also if you have cheap skimmer, not going to do it, that many fish

! What can do to help: TEST KIT! Good Skimmer, not a cheap one! and that sure is alot of fish! Possibly return the ones that are alot more agressive, not as interesting, and larger. Obiously you did not look around alot for info on fish size and there needs! Also if your fish store sold you fish that big, and didn't ask what size aqaurium/didn't care what size, then there probly in it olny for the money and possibly you should find a different store to buy fish from. Hope it all pulls through,
Evan