pretty well covered already
i would venture to say that kenyi (M. lombardoi) are much more aggressive than your frontosas.
the problem is that frontosas are a gregarious piscivore, whereas kenyi are algae-eating mbuna......so it would be extremely difficult to provide a proper diet for both fish in the same tank
plus, large male fronties could (and likely would) eat kenyi.
Sorry C-man i wasent clear, i ment for them to thrive they nedd to be in groups. and 12 in a 120???? thats only 10Gal. per fish, for Juvies OK but not for Adults
yeah, that is a bit overstocked.
what most people do is raise 10-14 juvies in a large tank like that and than thin out the males as they mature.
the goal (generally anyway) is 1-2 males per 7+ females.