Dems are more intolerant to their own kind than any other fish (they will also terrorize any fish with similar coloration/barring). They are best kept in a group of 12+ to spread out aggression amongst themselves, so 14 is fine for them.
Mixing Mbuna and Peacocks is also not the best thing, their diets & temperment greatly differ. It doesn't mean it's impossible, but it would be better to not mix them for the Peacocks sake.
My advice is to go with a Demasoni/Yellow Lab tank which is a proven successfull tank with nice coloration. I would do the 14 Dems and maybe 4-6 Labs, you can even substitute a few Acei for some Labs. Just remember that Labs & Acei will get much larger than the Dems and will outgrow the tank so may need to be thinned over time.
good luck