I remember hearing something long ago along the lines of the “Jewish ranks” in ww2 were if your parents were Jews and you were not you’d be in trouble however if your grandparents where and you where not you’d be fine, any merit to this?

Hey! I'm ASSUMING that what you're trying to describe is the concept of mischlinge, or people of mixed Jewish and German ancestry, in which the degree of ancestry could determine whether one was considered Jewish or German. Here is a past thread in which several people, including u/ColbyStein and u/gingerkid1234, discuss the criteria and ranking system.

If that's not what you had in mind, please let me know and I'll try to come up with something more relevant!