Flowerhorns are on a totally different scale of aggression as Blue Acara's. Hybrid cichlids tend to be more hyper-aggressive than pure bred counterparts. I think chances are very high that it would kill the Acara's. Blue acara's are pretty peaceful as far as cichlids go, you should look into other small peaceful(ish) cichlids to go with them. Rainbow cichlids would be a good idea. Large aggressive types won't be a good match unfortunately.