Q:Can i keep a group of afras (1M3F) in a 30 gallon?

A: Yes, you can easily keep a quad in a 30g tank if it is a single species only tank.   In fact, it is advisable to get the male even more girls!  You should be able to fit 1 Male and up to 6 Females together in that size tank, but closely monitor agression for the first few months.

 Q: Since i only have 3females, if they have fry and i grow out some females can the male breed with the females from his fry?

 A: I would do it to see how the inbreeding turns out. If they have a lot of disfigured fry - then I'd ditch the daughters.  It helps to know the background of the bloodlines - just to know how much inbreeding there has been in the past.