According to one of the reviews I've read for the the game:
Matthew’s friends are relatives of older Golden Sun characters, too. Tyrell is the son of Garet, while Karis is the daughter of Ivan. Other party members in Dark Dawn, too, have ties to previous characters.
^This gives me the impression that only Matthew, Karis, and Tyrell have any sort of relation to the previous heroes, but the other characters have ties to the previous heroes by OTHER means, like Rief being Kraden's student, and Eoleo being a part of the previous games and Briggs' son. Himi may related to Uzume, her being the only other Venus Adept to have the ability to see the future. Stella and Harumani though... I have no idea.
I'm kinda disappointed by the lack of Felix so far though, but maybe he's in Anemos with his
friend, Sheba, and they don't want to spoil the Anemos sub-plot. Or, if we assume: Matthew = Isaac, Tyrell = Garet, Karis = Ivan, and Rief = Mia, maybe Camelot is planning another game after this one that revolves around the descendants of TLA characters...? I dunno. GODDAMN IT CAMELOT JUST TELL US ALREADY!
Yeah, I'm going to have to get around to ordering in a US copy of the game myself. There's STILL no release date for Australia, all it says is: "TBA 2011". T_T So I'll just order in a US copy, if I can.
EDIT: Also, I've revived my old account at GSR. XD But it's been a little bit annoying there, since there's been a major influx of new people, now that Dark Dawn is just days away...
EDIT AGAIN: And today, in a completely unsurprising move, it has been revealed that Jenna is Matthew's mother, and Rief is Mia's son.