Complex sentence: The castle and estate then passed onto the Barclay family (also known as Craig) and it passed through successive heirs until the 14th century, whereupon it passed onto the Eglinton family on the death of Godfrey Barclay de Ardrossan, who died without leaving an heir.
Split into simpler sentences: The castle and estate then passed onto the Barclay family (also known as Craig) and it passed through successive heirs until the 14th century. Then it passed onto the Eglinton family on the death of Godfrey Barclay de Ardrossan, who died without leaving an heir.