Hal,
I would think TOM SAWYER might be the better book for seeking information on
Hucks origins, since it's the one in which Twain invented him.

In Chapter 25, Huck recalls that "pap and my mother . . . used to fight all
the time."   That's the only reference I can recall,  though there may be
more.

And there's always the problem that Twain could be so vague and breezy about
some matters--exactly how is Tom related to Sid, for instance?  Famously,
when writing HUCKLEBERRY FINN he was too lazy to go look up Tom's
girlfriend's name.  In her one mention in Huck's book  she is "Bessie."

Much more important, Twain's whole conception of Huck changed as he wrote.
Somewhere in TOM SAWYER the narrator mentions Huck's  slow mind, and in
general the boy is far less mentally agile than Tom in the earlier book.
Only in the last chapter, when Huck explains why he has fled the Widow's
house, does he really sound like the Huck of HUCKLEBERRY FINN.

Mark