Herbert Fitz Herbert, lord of Blaen Llyfni - Another son of Herbert Fitz Herbert?

I have been researching my Maxwell ancestry. In one resource, "The lineage of the family of Maxwell of Broomholm" it lists Herbert Fitz Herbert as the father of Herbert de Maccusweil >John de Maccusweil, Great Chamberlain of Scotland First Lord of Carlaverock, died 1241 and Aymer de Maxwell, Great Chamberlain of Scotland, died 1266. Married Mary de Mearns, daughter of Roland de Mearns a knight of the first Crusade. Aymer de Maxwell had Herbert de Maxwell of Pencaitland, Maxwell, Carlaverock and Mearns, die 1298 and Sir John Maxwell of Pollock, Ancestors of the Maxwells of Pollock, Calderwood, Newark, Auldhouse, Dargavel and Stainley in Strathclyde. It is Herbert de Maxwell line that I am in.

Herbert de Maccusweil took on the name Maccusweil because King David I granted Herbert the lands that had once belonged to Maccus son of King Anolf. There was a pond on the land or "weil". It was Aymer who shortened it to Maxwell.

My brother participated in a Maxwell Big Y DNA study, and we know we are in Aymer's line

Please give me your thoughts on the possibility that Herbert Fits Herbert, lord of Blaen Llyfni also had a son Herbert?

Laura Maxwell