It all depends.
The male Kenyi get super aggressive when they are fully grown in my experience. You might have trouble with them. I had a male Kenyi in a 180 gallon that tried to claim about 1/2 the tank for himself.. If there wasn't room for the others to retreat, they might've been injuried. When I put my hand in the tank, he would charge and bite it. I have had other Kenyi that were less aggressive, but they still claim a lot of space. So keep an eye on that, regardless of what you add.. I would not recommend a Kenyi in anything smaller than a 75.. Not to be harsh, just trying to warn you.
In general, yes, you can mix Mbuna and Peacocks. A lot depends on the temperment of the mbuna and the size of the tank.