Stephen's Lark's mention of Leo van de Pas's excellent geneology site reminded me that I haven't said much about Isabel of York, Richard Duke of York's sister, so I used the site to supplement the little I know about her, and thus can produce the following posting.
Isabel was of course the daughter of Richard of Conisbrough and Anne Mortimer and appears to have been born in the early years of their marriage, round about 1408 or 1409**. She was 'married' to Thomas Grey of Heton in 1412 as part of what appears to have been a deal to transfer the Lordship of Tyndale (then the property of Edward, Duke of York) to Grey's father. Due to the treasonable conspiracy of Richard of Conisbrough and the elder Grey (the Southampton Plot) this (marriage) arrangement was dissolved and Isabel was instead married (circa 1430) to Henry Bourchier, Earl (or Count) of Eu and later Earl of Essex.
** This assumes they didn't consummate their marriage until it was legitimised (1408). Since the detail of how they married, and when, is shrouded in mystery, it's possible Isabel was a little older.
Henry was the son of Sir William Bourchier and Anne of Gloucester, the extremely rich daughter and heiress of Thomas of Woodstock, Duke of Gloucester. (Anne was of course Richard of Conisbrough's first cousin. As well as being her father's heiress she had two dowers from the Stafford family, having married successive earls. She would make an interesting subject for a novel if anyone out there fancies writing one for her.)
The children of Henry and Isabel were:
William, who married Anne Woodville (or Wydeville or Widville). She was (need I say?) the sister of Queen Elizabeth Woodville. He died in April 1483. His son, also William, succeeded as Earl of Essex and lived long enough to serve at Anne Boleyn's coronation.
Henry, who married Elizabeth Scales, an heiress. After he died in August 1458 she married the well-known Anthony Woodville/Wydeville/Widville, later Earl Rivers.
Humphrey, who married Joan Stanhope, and was styled Baron Cromwell in her right. He was killed at the Battle of Barnet (1471) fighting for the Yorkists. Joan remarried, Sir Robert Radcliffe.
John, who married Elizabeth Ferrers of Groby and in her right assumed the title Lord Ferrers of Groby, though never summoned to parliament. He had a 'prolonged' law suit with Elizabeth Woodville over the Groby lands. His second wife was Elizabeth Chicheley of Cambridgeshire. He died 1495.
Thomas married Isabelle Barre, widow of Henry Stafford of Southwick the (Yorkist) Earl of Devon. After her death (1489) he married Anne, widow of Sir John Sulyard. He was Constable of Leeds (Kent) and was on a commission to investigate treason in Kent in December 1483. He died in 1491.
Isabel, the only daughter. Died apparently unmarried.
Edward, died 31 December 1460. (Battle of Wakefield)
Fulk, died young.
Essex was a 'backroom boy' for the Yorkists, occupying various offices without apparently becoming prominent in government or unpopular with Warwick or other hostile elements. He died peacefully in 1483. Nonetheless it's worth noting that the wars cost him two of his sons killed in action! His brother, Thomas, was of course Archbishop of Canterbury through the Yorkist period and a little beyond. (Their half-brother on their mother's side was no less a person than Humphrey Stafford, first Duke of Buckingham.)
Isabel of York died in 1484, during Richard III's reign. She was therefore in her early seventies, and so unusually long-lived for a member of the York family, even allowing for the tendency of the York males to have their lives cut short by steel poisoning. (In fact, when you think of it the only adult males of the House of York to die in their beds were Edmund of Langley and Edward IV. The rest either died in battle or were executed!) Isabel would certainly have had some interesting tales to tell and it's a pity that no roving reporter was around to interview her.