Complex sentence: In Rothbury he met Mary Hindhaugh, daughter of Robert Hindhaugh, who ran the local brewery and was one of a "large and influential family... since at least the seventeenth century".
Split into simpler sentences: In Rothbury he met Mary Hindhaugh, daughter of Robert Hindhaugh, who ran the local brewery. They were part of a "large and influential family... since at least the seventeenth century".