The problem of families in GUT is sometimes referred as an "Horizontal symmetry". There are two lines of work, roughly: those which get a continous symmetry, say SU(3), and then all the gauge malabars, and those which add a discrete symmetry, such as A4. Of course in both cases, a serious GUT should show everything embodied in a larger simple group. E8 has some value because it can go down to E6xSU(3), and E6 can lodge chiral fermions (but then perhaps this SU(3) does not work as it should, in more detailed examination) Other alternatives are just growing up SO(2n) until everything fits... You always have V+A currents you dont want, plus a bag of any of the usual problems in phenomenology.
Zee is the adecuate source to check if you want to look deeper in this topic.
This post imported from StackExchange Physics at 2014-03-17 03:38 (UCT), posted by SE-user arivero