I wouldn't put Blue Zebras in a 30g tank. IMO
they need more space, especially if you want to breed them. I wouldn't put them in anything less than a 55g.
Electric Yellows are iffy on tank size, but I would go with a 55g for them too.
If you want Mbuna for a 30g, look into Pseudotropheus saulosi. They stay small and while they are aggressive, they tend to be better than other Mbuna, especially in smaller tanks. The males are blue and females are yellow, so you'd have the same color combo, just with one species.
I would have a male and 4-5 females and thats it.