Complex sentence: Fraser-Mackintosh was wrong about the succession, for the present Chief descends from a yoounger brother of the famous Gillies-Donald MacBean, whose son William was of Pittourie in the parish of Alvie, Inverness-shire.
Split into simpler sentences: Fraser-Mackintosh was wrong about the succession, for the present Chief descends from a yoounger brother of the famous Gillies. This brother was Donald MacBean, whose son William was of Pittourie in the parish of Alvie, Inverness-shire.