Complex sentence: Richard Welles left a daughter Joan Welles, who married, first, Richard Piggot of London, and, secondly, before 1470, Sir Richard Hastings, a younger brother of William Hastings, 1st Baron Hastings.
Split into simpler sentences: Richard Welles left a daughter, Joan Welles, who first married Richard Piggot of London. Her second marriage was to Sir Richard Hastings, a younger brother of William Hastings, 1st Baron Hastings.