Very cool tank. I think they would be fine if left. I have a 125 with around 14 africans in it, varying from 2" to 4", some would say it is vastly understocked.....I had 4 2" in a 30 gal before moving to the 125 gal and adding the other 10 and the agression has really dropped off and my fish have never looked happier. I would leave as is for now if you are happy, and if you start to see too much agression, add/re-arrange rockwork and possibly additional fish at that point, to add to the crowd numbers.
Is your Zebra Obliquen showing any color? (wondering if you have a male and if he is showing color for you without any females present)