Complex sentence: He married Elizabeth Whitmore, sister of George Whitmore, also Lord Mayor of London; their other children included John Craven, 1st Baron Craven of Ryton, and Elizabeth, who married Percy Herbert, 2nd Baron Powis.
Split into simpler sentences: He married Elizabeth Whitmore, sister of George Whitmore, also Lord Mayor of London. Their other children included John Craven, 1st Baron Craven of Ryton, and Elizabeth, who married Percy Herbert, 2nd Baron Powis.