Any time I had jewel cichlids breed the only survivors were the jewel cichlids. Tankmates will be killed without prejudice. I even had to pull out a 10 inch pleco because the attacks were relentless and they would have killed it.
I have mbuna and peacocks with mine. They have their own zone in my 125g. The other fish show their respect, heh. When the fry are free swimming I put them in another tank.
Yeah, I think tank size is important here. My neighbor has a breeding pair in a 75 gallon. There is aggression, but no killings. I think anything less than that size would be fatal.