I don't think mixing Malawan and Tang cichlids together is the best idea. The Malawi fish like their PH a decent bit lower than Tang's do. I keep my Tang tank at around 9 and a Malawan tank I would keep at 8.3 or 8.5. Something to consider with your tank. Also, your Tangs would be a lot happier in their own 29g tank. You would probably get a lot more color out of them (and all of your fish) if they have more space.