Hi, I received your E-mail. Do ask your grandparents if they had any relatives in Rybitwy, near Polaniec, Poland,named Yaacov and Frida Knobel.The time line seems to fit.You can also get family information from the "Yad Vashem" Museum in Israel via the Internet.
You do seem to have had an illustrious and very famous great grandfather advocateconnected to Tolstoy.
Thank G-d all of us go back to Abraham, Isaac and Jacob as well as Sarah, Rebbeca, Leah and Rachel. ( Our Biblical ancestors). They are so famous they do not need last names.