I believe your issue is aggression and not doing research. All those fish are highly territorial. Adding 2 of the same angels is asking for fighting. Same with the 3 yellow tangs. Potters are incredibly tough to keep. I'd only get one if it is eating and looks healthy. I've had one for about 2 months now, but he's a pig and boss of the tank.
You're trying to add multiple fish of the same species which aren't supposed to be together unless the tank is huge or they're a proven pair.
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20 Gallon SPS reef
29 Gallon FW "fat catfish" tank
20 Gallon Long Dart Frogs "Zig" and "Zag"