You really need to double-check that water hardness - 59mg/l is way too soft for Rift Lake cichlids and most rainbowfish. Melanotaenia boesemani, for example, come from water with a GH above 300ppm.
Your pH of 7.8 is okay for rainbowfish and peacock cichlids from Lake Malawi, but they do need a GH of over 250ppm - ideally around 300-350ppm. If your water is soft, you'll need to add a Rift Lake water conditioner to increase the GH and KH. You can get this from most pet shops or online - it's usually a mix of calcium chloride, magnesium chloride, and calcium & magnesium carbonate, with a few other minerals.
If you get the water right, you can keep M. boesemani and M. lacustris with Aulonocara peacock cichlids. Just make sure your tank is at least 4 feet long and they'll be fine together. Keep the rainbowfish in groups of at least 6, and if you want to breed the cichlids, have 1 male and 3 or 4 female peacocks.
Also, make sure the rainbowfish get plenty of plant matter in their diet.