Complex sentence: From Catherine Cusack descended the Colley family who acquired the title Earl of Mornington, changed their name to Wellesley (they had Wellesley blood through Thomas Cusack's mother) and produced the 1st Duke of Wellington.
Split into simpler sentences: From Catherine Cusack descended the Colley family who acquired the title Earl of Mornington. They changed their name to Wellesley (they had Wellesley blood through Thomas Cusack's mother) and produced the 1st Duke of Wellington.