Complex sentence: On September 28 of that year he married Margaret Holland, daughter of Thomas Holland, 2nd Earl of Kent; two days later he was created Marquess of Dorset, and sometime that year he was made a Knight of the Garter.
Split into simpler sentences: On September 28 of that year he married Margaret Holland, daughter of Thomas Holland, 2nd Earl of Kent; then two days later he was created Marquess of Dorset. Also sometime that year he was made a Knight of the Garter.