Complex sentence: He succeeded his father in the earldom in 1891 and served in the Conservative administration of Arthur Balfour as a Lord-in-Waiting (government whip in the House of Lords) from 1903 to 1905.
Split into simpler sentences: He succeeded his father in the earldom in 1891. Lord Erroll served in the Conservative administration of Arthur Balfour as a Lord-in-Waiting (government whip in the House of Lords) from 1903 to 1905.