squeak-
I came up with eight, based on the following:
There are at least six separate people here (the children).
The relationships described are with each other (otherwise there would be at least six grandchildren).
Generation 1: Avrohom, a widower and Sorah, a widow
Generation 2: Yitzchok, Avrohom’s son who marries Rivka, Sorah’s daughter
Generation 3: Reuven, Shimon, Dina and Yehudis – Yitzchok and Rivka’s children.
a) one grandfather, one grandmother: Avrohom and Sorah
b) two fathers, two mothers: Avrohom, Yitzchok, Sorah and Rivka
c) six children: Yitzchok, Rivka, Reuven, Shimon, Dina and Yehudis
d) four grandchildren: Reuven, Shimon, Dina and Yehudis
e) two brothers: Reuven, Shimon
f) two sisters: Dina, Yehudis
g) three sons: Yitzchok, Reuven, Shimon
h) three daughters: Rivka, Dina, Yehudis
i) one father-in-law: Avrohom
j) one mother-in-law: Sorah
k) one daughter-in-law: Rivka
(this may be wrong, because by this cheshbon there should also be one son-in-law)