"Bonifacius marchio filius Teutonis…marchio…cum Alice cometissa filia qd. d. Petri marchio atque Theotone, Petro, Magnifredo, Hugone et Willielmo filiis eorum" donated property to "monasterio sancti Petri…in…villa Saviliani" by charter dated 21 Dec 1099. "Bonifacius marchio" appointed "filiis suos Maginfredum et Wilielmum adque Ugonem necnon Anselmum…et Anricum et Bonefacium minorem atque Odonem" as his heirs but disinherited "Bonifacium…incixie nominatum" by charter dated 1125. Documents pertaining to the divorce of Pedro II King of Aragon and Marie de Montpellier include testimony on their consanguinity, in particular "dominam Clemenciam amitam regine" (Clémence de Montpellier, sister of Guillaume [VIII]) declared that "Bonifatius marchio habuit tres infantes…Bonefacium et Guillelmum marchionem et Sibiliam. De…Guillelmo marchione exivit comitissa de Bigorra, et de comitissa de Bigorra exivit uxor Bernardoni comitis Convenarum…", although this last descent has not been traced. "Marchiones Wiliemus et Manfredus filii marchionis Bonifacii" promised not to construct castles in a certain location by charter dated 1135. "Marchiones filii domni Bonefatii…Manfredus, Wilielmus, Ugo, Anselmus, Enricus, Oddo Bouarius" donated property to the monastery of Staffarda by charter dated 9 Dec 1138.
Marchese di Busca: a charter dated 22 Dec 1142 records the division of territories agreed between "Marchiones de Vasto…Mainfredum, Willielmum, Hugonem, Anselmum, Heinricum, Bonifacium et Oddonem filios quondam Bonifacii marchionis", under which Guglielmo took "marchionatus de Busca".
Signor di Rossano 1155: the bishop of Torino granted "castro Rosiane" to "dominum Guillelmum marchionem filium Bonifacii quondam" by charter dated 1155. "Willelmus marchio filius Bonefacii marchionis quondam bone memorie" donated property at Scarnafigi to the monastery of Staffarda by charter dated to before 1156, witnessed by "Mainfredus marchio, Oto Bouerius marchio…".
The name of Guglielmo's wife is not known. 1
Research Notes: