there are many other fish that you can choose from. let us know what you like, and i'm sure you'd get a number of great suggestions.
both the zebra and the yellow would appreciate conspecifics.
don't try to get too many jewels, as they will pair up, and the pair will become very intolerant of tankmates once they spawn. though i don't have experience of keeping them separately, having kept mbuna and jewels separately, i doubt that even the robust mbuna are not strong enough to coexist peacefully with a pair of breeding jewels. even though 75g is a pretty big tank, the jewels will probably claim half of the tank, making the rest of the fish very unhappy.