Short answer: I don't think it's ever definitely stated, but that is the assumption most people make
Long rambling answer: Jake makes mention his family is Jewish in the distorted history of MM3, apparently on his father's side, (which some counter doesn't make him Jewish, cause it is passed down the mother's side, but I don't know wtf that's all about.)
How they are cousin's isn't really spelled out: I know Rachel and I think Jake are said to resemble their own fathers, and that "you can tell" the two are cousins. But that's a weak argument that their dad's are brothers.
The best reasoning I can make is that Naomi is not close Saddler's parents, so the family tie of all three cousins is Rachel's dad and either of Jake's parent's, but because Jake's mom is the one that went straight to Grandpa G's funeral and seemed most effected it seems Jake's mom is his descendant, and Rachel isn't related to Grandpa G(and I don't believe Saddler's family was there either) I seems most likely that it is indeed Jake's Dad and Rachel's dad are brothers.
So if Jake's dad is Jewish, and that wasn't just a factor of the warped history, that Rachel's dad should be too, and so should she, unless you take that passed down mother's side thing into account and again: I don't what that's about.
My hesitation with all that is Rachel always sid she was too tall for gymnastics, yet she resembles her dad who was really good at it. what???
sorry not simple response to simple question
