Thanks for sharing your mother's touching story.
David Solly Sandler from Australia published a book on the Pinsk orphanages: "The Pinsker Orphans; The life and times of the children from the three Pinsk Jewish Orphanages in the 1920s", published by David Sandler, 2013. You can find the book in Amazon.
In addition the Brest Archive in Belarus holds a numerous number of files on these children. The files include questionnaires, applications to travel abroad and more. The documents are in Russian, Polish and Yiddish, so exhausting them is very hard. Years ago I tried to employ someone to find info on 3 orphans who came to Israel in 1923, also under a false family name, and nothing was found. In the end I established their identity thanks to press news: a cousin from Russia tried to trace the children in 1937. Perhaps you will have the same luck?
Tsukey Yam, Israel