Aggression wise - it will depend upon the species. Some of the Cynotilapia species are more aggressive than others. With the right amount of numbers and correct sex ratio - it is quite easily done.
Breeding wise - like Kim stated, most people recommend against it. It can be quite risky to do. I mix multiple species together to breed, but I also watch my fish carefully. Knowing who is "showing" for who is crucial - and "if in doubt, let'em spit 'em out" (I don't keep the fry).
This really depends on what you want these fish to do. If you just want to look at them and have a great tank, then mixing is fine. Like Kim said, if you plan on breeding them, you can't trust that just because a female Jalo has a mouth full of babies that they came from your Jalo male. In my show tank I have many different kinds of cynos and they are great together. I don't keep any fry from this tank, if I want fry I move a group to a 30 and wait. Like spyder said, pay attention to the ratios and enjoy.