Medlands says William was born c. 1131-1133, which suggests that *most* of the birth dates in this section have been jacked around. Robert and 'Guillaume" (another William) are listed as his children, but no Ralph, no Henry and no Mabel.
https://fmg.ac/Projects/MedLands/enguntlo.htm#WilliamMauduitdied1194
Per this page, it was William's *sister Matilda (Maud)* who married Hamo FitzMeinfilin. (Almost all Matildas went by "Maud" for everyday by the twelfth century - the Empress Matilda being one of the few who might stand on ceremony.)