If anyone here lives in Yerushalayim, maybe they can help you.
The yeshiva he founded, Yeshivat Nahar Shalom, is (according to the Internet) “located on a small alley in the back of the Mahane Yehuda Shuk and is physically difficult to get to.”
But if you go in there, I’m sure the Rosh Yeshiva could
tell you his grandmother’s name, if it’s that important.