Complex sentence: He is an advisory trustee of the family's principal philanthropy, the Rockefeller Brothers Fund and he sits with David Rockefeller on the board of the World Trade Center Memorial Foundation.
Split into simpler sentences: He is an advisory trustee of the Rockefeller family's principal family-run philanthropy, the Rockefeller Brothers Fund. He sits with David Rockefeller on the board of the World Trade Center Memorial Foundation.