According to SP Vol 8, p. 480 they had a dau. Isabel who "m. c. 1386 Sir John Wemyss of Kincaldrum, by whom she became the ancestress of the present families of Wemyss".  But nothing can be found of this Isobel in the later narrative.  Wierd!

However Bruce McAndrew in his “Scotland’s Historic Heraldry, p. 163, shows that the Isobel concerned was this Margaret’s granddaughter and was also known as ‘Elizabeth’.