http://en.wikipedia.org/wiki/Anoa'i_family
Basically, it breaks down like this:
The original 5 siblings are Afa, Sika, Junior, Tumua, and Vera Anoa'i. Their parents considered Peter Maivia a "blood brother" and the kids considered him an uncle, which is where the Rock and his dad come in.
Afa's sons:
Samu, Afa Jr. (who's in DSW now I believe), LA Smooth, and daughter Monica who married Gary Albright.
Sika's sons:
Rosey, Joe Anoa'i (who currently plays college football)
Junior's son:
Yokozuna
Tumua's son:
Black Pearl (wrestles in Rikishi's Italian fed)
Vera's sons:
Tama (from the Islanders), Rikishi, Umaga
Apparently boxer David Tua is also related somehow, but I'm just happy to finally get the wrestling side cleared up.