Complex sentence: Together with its ancestral possession, the County of Schaumburg, the family also ruled the County of Holstein and at times also the Duchy of Schleswig until 1460--and the sub-county Holstein-Pinneberg until 1640.
Split into simpler sentences: Together with its ancestral possession, the County of Schaumburg, the family ruled the County of Holstein. Subsequently, the House of Schaumburg were also counts of Holstein and at times also dukes of Schleswig until 1460--and of the sub-county Holstein-Pinneberg until 1640.