The official English site for Golden Sun: Dark Dawn has been updated with character information: http://goldensun.nintendo.com/. Click through for full details, but here's the summary:
Party: Matthew (Isaac's son), Tyrell (Garet's son), Karis (Ivan's daughter), Rief (Kraden's apprentice), Sveta, Amiti (possibly Pier's descendent?), Eoleo (Briggs' son), and Himi (daughter of Susa & Kushinada (from Izumo quest in TLA)).
Antagonists: Arcanus (Alex with a mask), Chalis, and Blados.
Isaac and Kraden also make appearances in the list. We know from the trailer that Garet is also in the game, though he is not listed on the official site.
I would also recommend that everyone check the GSS homepage on the morning of Monday, November 22. I'm not yet allowed to say why, but I assure you it will be worthwhile (and time-sensitive).
Finally, there will likely be a few hours of downtime this weekend as the GSS forums and website are upgraded.
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