Guillaume was the son of Paien de Coësmes and Julienne de l'Écluse. The date and place of his birth have not been found.
His wife was Héloïse le Franc. They were married, but the date and place have not been found. Their five known children were Briand (?-?), Payen (?-?), Mahaud (?-?), Isabeau (?-c1320) and Jeanne (?-?).
Hervé de Coësmes |
Brient de Coësmes |
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Emma de Vitré |
André II de Vitré |
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Ennoguen de Léon |
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Philippe III de Pantin |
Raymond de Pantin |
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Nicole de Machecoul |
Olivier I de Machecoul |
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Mathilde de Coché |
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