Well done, Gaie. I should have thought of that.
Kravitz is derived from the Polish word for tailor = krawiec.
The Yiddish word is shneyder, and that is the more common surname, spellt Sznajder in Polish.
Do you know where and when Michael and Fanny married?
My thinking is that Fanny come from Poland, i.e. not Kovno, where Shneyder is the more common name, although I have also seen Kravets and Kravitsky.
Justin