Regal Worm of Slopp said:and yes, most of the others have about as detailed (if incredibly unlikely) backstories
Okay - one last suggestion. Ask them to come over for a "character workshop" party or something. Have some snacks and try to have each player find one or two "hooks" in their backstory that they can focus on during the role-playing aspects of the game. Similar to the ideas you got from Djeta and/or me or whatever ideas you come up with on your own.
Just keep it simple to start - one or two little details that will come out during play. That should be a great start.
Then, separately, talk to your DM and mention that you've really taken an interest in trying to get people to RP their characters better. In return, you'd like positive feedback either during or after the session on what the DM thinks is improving. Positive feedback, and maybe a little extra XP, should help motivate the group.
Good luck!