As I understand it from viewing the series a few times, and seeing the family tree in the DS Almanac (chuckle)
as well as a few websites...
[spoiler]Quentin had two kids, a boy and a girl... Now of course the boy died, via the curse placed on Quentin. The girl, Lenore, lived. Lenore later married and must have had at least two daughters: one married a Jennings, the other a Haskell. So - Tom/Chris/Amy were cousins to Joe. However, that also means that for Tom, Chris, Amy *and* Joe...Lenore was their Grandmother, and Quentin was therefore their Great-Grandfather (even though they probably wouldn't have known that, since Lenore wasn't brought up a Collins - but she still had the same genes to pass on the curse and whatnot, of course
) They all have traces of Collins blood, but not directly.[/spoiler]
Whew...hope I figured that out right. LOL