So I was just wondering what other fish species can I keep in my 75gal tank? Here's a list of the fish i currently have: (2) zebra obliquidens, (2) yellow labs, (2) red zebras, (2) jewel. Total of 8 fish in the range of 3"-4"
The locations of the various locations doesn't matter as much as there temperment, size, needs, etc. So as long as they are compatible ( i.e. Same aggresion and needs) then they should be okay. And as long as the non-cichlids can hold there own then they should be good.
You certainly have room for more fish but there are a couple of issues I see with your current stock. The first is the Jewels are a riverine species that shouldn't be kept **** Mbuna. The Jewels require a different diet, different decor & different water parameters to the rift lake fish. The second is the Zebra Obliquidens are a very peacefull fish. So peacefull that they don't usually do well in a tank stocked with Mbuna. You can try them & see how they go but normally they need to be removed when the Mbuna mature & start showing thier true levels of aggression.
You can mix fish from the different lakes so long as you take different habitats, diets & aggression levels into consideration. It's not wise however to try to mix fish from the different lakes if you are going to be focused mainly on the mbuna. Most Tanganyikans & Victorians are insectivours or carnivours, with a few exceptions. Mbuna are predominantly herbivours & can suffer various intesinal illnesses, including Malawi Bloat if there is too much meaty foods in thier diet. If you were focused on Haps then you could mix fish from teh 3 lakes without too much trouble but as you have the Mbuna, I advise you to stick with just other Mbuna species & either Synodontis catfish or Common Bristlenose Pleco.
I would remove the Zebra Obliquidens & the Red Jewels then I would add another 2 Red Zebras & 2 Yellow labs then introduce 4 Maingano, 4 Afra, 4 Socolofi (there are other stocking lists that would work). That would give you a total of 20 fish & leave you room to introduce 1 BN Pleco or a single Synodontis.