I think Aubry is the son, not the brother of Geoffroy, Seigneur de Château-Landon, Comte de Gâtinais
1. GEOFFROY [I] de Château-Landon, son of --- (-after Nov 991). Seigneur de Château-Landon. Comte de Gâtinais. "Gausfridi comitis Wastinensis" subscribed the charter dated to [985/87] under which "Teduinus" donated "alodum…Vileta…in pago Wastinensis" to the abbey of Saint-Père de Chartres for the souls of "patris sui Adelardi et matris suæ Eldegardis"[176]. m as her first husband, BEATRIX de Mâcon, daughter of AUBRY II Comte de Mâcon & his wife Ermentrude de Roucy. A manuscript genealogy, dated to the early 12th century, records "Letaldus comes Vesoncius et Umbertus comes Marisconensis fratres…ex Letaldo, Albericus…ex Alberico Beatrix, ex Beatrice Gosfrido de Castello Landonensi"[177]. André de Fleury’s Vita Gauzlini records that “Albericus comes Nandonensium” donated “Alodum in Altissiodorensi territorio” to Fleury and that “Beatrix Nandonensium comitissa” donated “prædia”[178]. She married secondly Hugues du Perche, her second marriage being confirmed by the charter of her son "Albericum illius supradicti Gosfredi filium et heredum" dated 26 May 1028 (see below) approved by "fratribus ipsius Alberici, filiis Hugonis Pertice…Gosfredo et Letoldo"[179]. Geoffroy [I] & his wife had one child:
a) AUBRY [Alberic] de Gâtinais (-before 8 Mar 1030). Francon Bishop of Paris agreed with "Albericum illius supradicti Gosfredi filium et heredum", concerning a prior grant by the bishop's predecessor to "Gosfrido comiti Landonensi castri", with the approval of "fratribus ipsius Alberici, filiis Hugonis Pertice…Gosfredo et Letoldo", by charter dated 26 May 1028[180]. He succeeded as Comte de Gâtinais, Seigneur de Château-Landon. André de Fleury’s Vita Gauzlini records that “Albericus comes Nandonensium” donated “Alodum in Altissiodorensi territorio” to Fleury and that “Beatrix Nandonensium comitissa” donated “prædia”[181]. https://fmg.ac/Projects/MedLands/cfragobs.htm#GeoffroyGatinaisdied991
