I agree that you shld stop your dad from buying anymore fishes for now. If not, you are just wasting those precious and innocent lives away just like that. Water parameters must be main problem.
i used to have bta in my tank with mh light and it would climb to the top for sun-tanning but when i change to par38 recently, it crawl and hide away from light.
My percula clowns were very aggressive with anemone in the tank and after i remove the anemone, they were more friendly and a little timid when my hands goes intot the tank for maintenance.