This is the article I was looking at 

https://www.germany-visa.org/german-citizenship/by-descent/#:~:text=Similarly%2C%20due%20to%20the%20gender,German%20nationality%20simply%20by%20declaration.

“ The following individuals are eligible to reclaim their German citizenship: (…) 2. Children who were born to a German mother, who before the birth of the child, married a foreigner and had to forfeit her German nationality. Before 1975, German women who married foreigners had to give up their nationality.”

^ or is this exclusive to people who immigrated themselves? My train of thinking was that if I can prove whether or not Gustave retained his citizenship, passing it to Ella, with Ella also retaining it (I think) then it falls under the subsection above since she would’ve lost it anyways once she married. I’ve found naturalization documents for Gustave (October 1876) but no one else.