Been there, done that with no problems between the two pairs. Try to encourage them to set up on opposite sides of the tank by leaving few good spots in the middle, and put some kind of visual divider (like a slab of slate or big bushy plant) between the spawning sites. Of course, you still COULD have trouble — cichlids are rather individual, after all. Good luck!
It always depends on the specific nature/personality for the actual fish purchased as seen in the posts above.
On a general personality note it should be O.K. but not great, do try to cut the tank in half with something as monkey toes posted if you do go through with it.
If things get too tense in my 55g with Malawis I just take the plants along the back down the middle so the angry fish can't easily see the other fish who is ticking him off and it seems as though the angry fish is satified that he chased the "intruder" away.
thanks for the advice, its what I was expecting. I'll just keep a close eye on them. Dont suppose introducing them all together when they are young will have any effect (like having puppies and kittens together-- I know thats a stretch)