Complex sentence: A daughter of the Countess and Earl of Carrick was married to her paternal grandfather Uilleam II, Earl of Ross; making Uilleam II their son-in-law and by some definition Aodh, their grandson of sorts.
Split into simpler sentences: A daughter of the Countess and Earl of Carrick was married to her paternal grandfather Uilleam II, Earl of Ross. Making Uilleam II their son-in-law and by some definition Aodh, their grandson of sorts.