Actually I would remove a species. Three is good for a 55G.
Malawi are harem breeders so it is a good idea for the health (and survival) of the females to have four of them with one male.
Do you mean Maleri the peacock? Or Marlieri the julidochromis?
Peacocks crossbreed, so you would not want two peacock species in any tank. Also, once you mix them you cannot with 100% certainty ID the females correctly since they look so much alike, except maybe blotch females.
So...I would take out one peacock species and add females to the others until I had 1m:4f. And I'd double the synodontis. Petricola, labs and acei like to be in groups of 5-6.
If you are talking about julidochromis, those are Tangs and might prefer to be in a tank with other Tanganyikans.