Can't really see the gang getting to much hate from other crime orginizations.
Maybe each protag will also have a separate antag to their own story line.
Franklin = Gang Related, Maybe Lamar (is that is bros name, gta seems filled with traitors). Michael = guy banging his wife, also a snitch. Trevor = This is a hard one to make up, hmmmmm. Maybe another cop. --- I'm probably the least f***ed in the head person in the world. I swear to god m8 everyones f***ed in the head.
Well, in Trevor's trailer, you can see him beat down a Lost member with a baseball bat, then shoot the hell out of a Lost car with a shotgun. --- "They sat a while in silence, they turned at last to me... ...We will call you Cygnus, the God of Balance you shall be" -Neil Peart
They'll do a M night shamaladingdong twist where for the whole game, trevor is the unpredictable one but then it turns out Michael rats on them for witness protection and then you got to kill him. --- <PSN> britz02