Fed gov will move to charge him with violating Civil Rights and subject him to another trial even if he is found innocent of the first one. If he beats that, the black groups will fund the Martins to file a civil suit for wrongful death. In a civil suit, you are presume guilty and must prove your innocence. By the time all is done, Zim would have legal fees for three major trials.
If Zimmerman is NOT tried because of stand your ground (which I hope and pray he’s not because he’s innocent), the family CANNOT sue civily. The law prohibits it. :)