Judging by one of the screenshots, I'd say we find out in VV3!

Yes Arnie! And as you said they are all adults!! It could be them!!

But they are 8!!!

Maybe one fell overboard during the storm?

EDIT: Perhaps there could be an event where the eighth villager appears from the sea in a similar manner to the 'Old Friends' are also washed down the waterfall in VV2?

EDIT: Yes maybe, but who are the 7 in the north part of Isola? Where they come from? (in the picture)

One of the pics shows them on a raft during a storm. Maybe they were blown off-course and washed up on the north shore because of that? Or they've got a pretty poor sense of direction - they set out to go back south, but ended up north! Since Isola is a magic island, compasses probably don't work.