Complex sentence: Married to Lady Jean Keith, a daughter of William Keith, 7th Earl Marischal at the end of September 1669, the couple had two children: a son, also named George who went on to become the 4th Lord Banff; and a daughter.
Split into simpler sentences: Married to Lady Jean Keith, a daughter of William Keith, 7th Earl Marischal. The couple had two children: a son, also named George who went on to become the 4th Lord Banff; and a daughter.