Can you identify this disease?

[JML27]

Hi, reefers! I have had 2 fish die that have had this same white "scar" on their heads/body (I uploaded a picture below). Can anyone tell me what this is and how to treat it? These are the only 2 fish where this was visible but I have had 3 OTHER fish die too -- something is definitely very wrong and I cant tell what. All my water tests are fine so it must be a disease, parasite, etc. of some kind. Thanks!

 

[JML27]

Sorry I left something out...
The other 3 fish that died, before I saw this white "scar" I was concerned that my vlamnigi tang was killing the other fish. I didnt ever see it but all the others died. The only fish that remains is a coral beauty and the vlamningi. Are vlamingi tangs aggressive to the point where it would kill other fish (not tangs and the other fish were in the tank before the vlamingi)? Do I need to get rid of him?