First, let me just say this game is excellent! I've been wondering some things about some of the families:
1.) Who might Griff's parent be? Biff's daughter, Tiff Tannen or Biff Jr.? Biff Jr. was Biff's son in an early draft of BTTF Part II and the cartoon (Which probably isn't canon.). From what I've read on Futurepedia, Biff Jr. is about 15 years older than Griff, which would make him a teen parent and that makes sense for a Tannen.
2.) Is Biff illegitimate? From what Doc said, I'm just assuming that after his mother had him she either died or dumped him on Gertrude Tannen's doorstep.
3.) Assuming that Gertrude Tannen is Buford Tannen's daughter-in-law, do you think we'll ever meet or learn anything about Buford's son/Kid's father? I wonder if he bullied William McFly? And what about a teen or adult William? I wonder if his personality was like Marty's or if he was a wimp like Artie, George, and Marty Jr.? It seems like Marty is the only McFly without a Tannen bully.
4.) In the cartoon episode "A Friend In Deed," Jennifer's grandfather Parker is alive in 1992, owns a ranch, and is called "Pete" (As in "Peter Parker!") by the sheriff. Get Tannen contradicts this.