Those are tropheus not demansoni.
Demasoni
View attachment 195626
Tropheus duboisi
View attachment 195627
Demasoni are really aggressive but very nice looking. They need to be in groups of 12+ or they kill each other down to 1.
The best dwarf mbuna for that size tank are pseudotropheus saulosi. Males are black and blue while females are bright yellow. It makes a nice species tank.