Well first things first.. there should only be one damsel in there at most right now. Your tank needs to cycle first. The water becomes toxic to fish during the cycling process. A tang should definitely not be in there right now, they create a lot of waste.
What kind of filtration do you have? You absolutely need a protein skimmer if you do not have one. I recommend the Aqua C Remora. I have a Aqua C Remora pro on my 72 gallon that has been fantastic.
I also recommend getting an additional canister filter, such as an Eheim, and run media such as Chemi-pure in that, but that can wait,.. if you don't have a protein skimmer, get one immediately if you want to have any hope of keeping those fish alive.
How much Live Rock/Live sand do you have? Are you using tap or RO/DI water?