Theoretically, yes. N. mult gets to only about 1.5 inches, while N. brevis gets to only about 2 inches. Total length for these 2 species in pairs: 7 inches max.
I'm a bit of a stickler, and believe that most fish, esp. cichlids, really prefer and deserve a little more room. I'd give these guys at least 20 or 30 gallons to roam around in, as they're fun, lively fish when they're not hiding in shells.
Consider it... I think you'll enjoy watching these fish more if they have room to roam.
Yes, an Aquaclear 150 is filtration enough for such a tank, but I recommend a Penguin Mini or a Penguin 125, as these have biowheels to enhance and maintain biological filtration. I have a Penguin 125 on my 10 Gallon and it does a bang-up job (great).
I'd also advise a little more sand (1.5-2 inches) if you're going to go with that as a substrate. But also consider crushed coral. This is easier to clean with a gravel vacuum, and will still increase the pH a bit. Of course, crushed coral in the filter is the best way to ensure a constantly high pH. Lake Tanganyika cichlids actually prefer an even higher pH than the 8.0 you mentioned... from 8.4-9.2 or so. If you can increase the pH naturally with a mesh bag of crushed coral in the filter, great!
HTH