Complex sentence: Montagu was one of the younger of the eight sons of the judge Sir Edward Montagu, of Boughton, Northamptonshire and Elizabeth Harrington, and the grandson of another judge Sir Edward Montagu and his third wife Helen Roper.
Split into simpler sentences: Montagu was one of the younger of the eight sons of the judge Sir Edward Montagu, of Boughton, Northamptonshire and Elizabeth Harrington. He the grandson of another judge Sir Edward Montagu and his third wife Helen Roper.