well I only have one other tank thats a 20 gallon. and right now it has 8, 2 inch long babies in it. so letting her spit them out naturally is not an option as the young in that tank are large enough to eat the newborn so I'm going to force her to spit them out into a breeder net as I have about 3 times before...
When growing out fry for selling you'll need additional tanks to accomodate fry and juvies of varying sizes. Larger fry and juvies can be brutal toward and even predate their smaller brothren.
What's the plan when the fry become too big for the breeder net? (which isn't the safest way to go about as opportunistic larger mbuna in the tank may be capable of sucking the fry right through the mesh). By the time they're in need of larger accomodations they may still be too small to fend for themselves in your 20gal. Though, with that said, 2"-2.5" is pretty much selling size for the ones you've got in there already.
When I used to trade in mbuna fry to the LFS I'd cycle them through several concurrent tanks, starting them out in a 5gal maturity tank (new fry), then move them to a 10gal (small juvies), then finally to a 55gal (selling size juvies).