I would put a divider in for a couple of weeks and then take it out and watch for aggression. If still to aggressive put it back in for a couple more weeks.I had to do this for about 6 months before I was able to get them to breed or even live together with out killing each other.The parents of your fish had to be the most aggressive Festae maybe the most aggressive fish I have ever seen and I have umbee,dovii,trimacs,saggitae and a lot of other very aggressive cichlids.Just don't give up on them.