aquarium help

Hello, I had a quesiton, could I have two sailfin tangs, a unicorn tang and a yellow eye kole tang together in the same tank. Currently In the tank is one sailfin tang that has been there for about three months alone.

Please help, i have a hugh ammonia problem and dont know what to do. Starting from the beginning, i have run the tank for 6 months with no issues, but about two weeks ago i stupidly stirred up the sand bed after 6 months on it being untouched with a vacuum (first mistake) for the week after...