The Verdict: Need More Info
It turns on whether your family left Germany because of Nazi persecution, which would put you on a far more generous route. Take the Germany Historical Displacement quiz first, then come back here if it does not fit.
If they did, Article 116(2) of the Basic Law or Section 15 of the Nationality Act applies: no generational limit, no deadline, no residence or language requirement, and no harm done by an ancestor taking another citizenship.
The year they left and where they went usually settle it. Departures between 1933 and 1945, particularly to Britain, the United States, Palestine, Shanghai or Latin America, are worth investigating even if the family never described them that way.
Nothing is lost by checking in that order; the ordinary descent rules will still be here.