William...inherited an extensive fief held of the Honour of Coupland, served as Castellan of William Fitz Duncan's castle of Egremont in 1138, and was Governor of the Castle of Lancaster. [Ancestral Roots, line 88]
No source gives a first marriage to William. But the fact that Gundred was a widow at the time she married William, and her 1st husband died in 1153, would dictate that William's first child Gilbert, attributed by Ancestral Roots as a possibility, was born to another mother than Gundred.
Avice's birthdate is about 1145 according to some, but if Plantagenet Ancestry is right in attributing her mother to be Gundred (Ancestral Roots gives no mother), then an 1155 date would be much more likely. This also involves making subsequent descendant birthdates a bit later as well.