Not trying to be 'mean' here but your tank isnt 100g, its 121 x 41 (46 on the bow) x 64 (including the hood, so make it 60). Making more around 80usg.
Making just large enough for the 2 severums plus the brasiliensis as its lower dwelling and the rainbows, adding the GT was daft IMO, you dont have to have one you know. You make the comment on another thread, that I have more stocking than you, well yeah, I have a larger tank than you, that not being the point, what works for one person, doesnt necessarily work for another.
The GT and BA shouldnt be togther, the GT will (unless extremely placid) kill the BA or worse still hybridise with it, maybe thats what your hoping for
So IMO and it is just MO, you either need to rehome the GT or rehome the rest of the fish, add some dithers, you have the rainbows, well lets see how that works, and possibly the BN will be fine.
Like I say, Im not having a go, but some times you need some perspective on your tank as you think its larger than it is and just because other people mix certain fish, doesnt make it recommended or advisable.
Edited to add: It MAY work out, these are cichlids and its down to their individual temprements, but I just think you should be prepared for it NOT to work, is the point Im tryng to get across, I get in trouble sometimes for coming across as too negative, its not my intention.