The anemone may actually weather the coming ammonia spike better than the clowns do: it'll shrivel, expelling water, until the ammonia goes away.
You need tests for alkalinity, nitrate, ammonia, Salifert is a good brand, easy to use. Feed very sparingly: be sure the food is all consumed. Don't force anything to do anything. You may want to turn the pump off for just a little to be sure the clowns get all the food there is with none left over. Keep Prime on hand, follow directions, and meanwhile read the sticky atop this forum with the blinking red arrow. That will tell you a lot of what you haven't asked yet. Keep the food very, very tight: that will slow down and moderate the chemical reaction that's coming. Hopefully it will be mild, and everything will survive. Clowns are tough. Watch your salinity and keep it at 1.024 without fail: you may want to draw a line on the tank wall to tell you where the water level is when it's perfectly 1.024, and then make up any evaporation with fresh water twice a day until you get an autotopoff unit. You've sort of been set out on the high wire, handed a pole and told to watch your balance, but if you're just careful and keep your levels steady you may get through this.