Good advice by Razzo.
I've got a bristlenose in my tank and he's doing fine, none of the mbuna bother him at all, in fact they scatter away whenever he swims up to an algae wafer or a cucumber that they're ganging up on, and he keeps the tank clean as well.
I would rehome the kenyi (not only will they get too aggressive, but it's also recommended to keep them in a 75gal minimum, because of size and aggression), bump up your existing groups (1 male to at least 3, 4 females as suggested above, labs do better in groups of at least 6) and look at species Razzo has mentioned.
Also iodotropheus sprengerae make a good tankmate, as they are one of the less aggressive, smaller mbuna. If you're looking for blue, try cynotilapia "white top hara" as well, males get really nice vibrant light blue color with dark bars, while females stay blue.