Your tank section lists the following as your stocking list:
4 Labidochromis caeruleus
1 Melanochromis auratus
1 Melanochromis cyaneorhabdos
2 Pseudotropheus crabro
3 Metriaclima lombardoi
1 Pseudotropheus sp. "Aggressive Grey Head" i think this is what it is
To get the fish to breed you might want to reconsider your stocking list.
The three most aggressive mbuna that I am aware of are the auratus, lombardoi, and crabro. Generally it is recommended that one keep a single one of these types of species in set ups of at least 75 gallons, and even then they can be a real hassel.
Having two of the crabro might be a problem because mbuna are best kept in groups with several females per male in order to reduce aggression issues.
Also two melanochromis species could create an aggression problem because they are so closely related and have horizontal barring they will view each other as threats.
To breed these fish, it would be easier if you had fewer species but in greater numbers. For a 55 gallon your best bet are probably the yellow labs and pseudotropheus sp. and maybe the cyaneorhabdos? I haven't kept those last two species so it would be better to wait for more advice.