Actually, I believe it is the same Laura that pops up over and over.SPOILERIn the 1897 story, Laura (Edwards wife) remembers Barnabas from when she was married to Jeremiah Collins in the 1700's.
As for Joe Haskell, the family tree I saw does indeed indicate that Joe is a descendant of Quentin's daughter, the surviving twin Lenore. She apparently had two children, one of which married a man named Jennings, who was Chris/Tom/Amy's mother, and one of whom married a man named Haskell, who was Joe's mother. At this point, however, neither Joe nor Chris know they're descendant's of Quentin's.
It's never stated clearly how Joe is related to Chris. I've seen a lot of family trees, but they're often created by people who take liberties with the facts and throw in names and characters with nothing to back them up.