Complex sentence: His son Barry (Shalom Dov Baer) became alienated from the Chabad movement and claimed that the official Chabad library was a family heirloom and as the previous Rebbe's sole grandson, he claimed ownership of it.
Split into simpler sentences: His son Barry (Shalom Dov Baer) became alienated from the Chabad movement, and later claimed that the official Chabad library was a family heirloom. As the previous Rebbe's sole grandson, he claimed ownership of it.