Well, you asked for an opinion. Mine comes from 22 years experience in
bonsai and studying with some world-class bonsai artists.
They are your trees & you are free to style them as you please. If you
are dissatisfied with my opinion, post your pictures at the Internet
Bonsai Club, or even better, take your trees to a meeting of the
nearest bonsai club. Either way, you will get even more expert
opinions than mine.
If you like the piece of driftwood, place it to one side of the tree,
not between the two trunks. Also, treat it with a wood preservative,
like MinWax Wood Hardener. Otherwise, leaving it on damp soil will
cause it to rot.
I am not concerned that the long bare trunk will cause harm to the
health of the tree. It just doesn't look right artistically. The two
trunks need to look alike, as if they have both been growing in the
same place, under the same conditions.
Try to get hold of Deborah Koreshoff's book, Bonsai: Its Art, Science,
& Philosophy. She has a whole section on two-trunk trees. Also, take a
drive out in the country and look for twin-trunk trees, & see how they
actually grow.
Iris