I am descended from Oliver St. John (c. 1300 - c.1373 of Fonmon, Glamorgan Wales who married Elizabeth de la Bere, daughter of Sir John de la Bere.
The Cornwall Records office has two 1371 Arundel deeds. The first of these deeds is a trust deed from John Arundel, Sr., to Richard Deuysier and Matthew Bodrygy, trustees, involving the manor of Conerton and other properties (except not the manors of Lanherne and Treloy) from John Arundel, Sr., Lord of Lanherne with his son, John Arundel, Jr., Lord of Treloy, as co-granter to hold for the benefit of John Arundel, Sr. during his lifetime and after his death to the heirs of John Arundel, Sr., by his wife, Elizabeth, daughter of Oliver de Carminou. (Cornwall Record Office AR/20/2)
https://kresenkernow.org/SOAP/detail/09daba34-3920-4052-b54a-3d8aaa389abd/?tH=[%22AR|20|4%22
The second of these 1371 deeds is from John Arundel [Sr.] to the same trustees as in the above-mentioned deed involving the manor of Lanherne. One interesting item in this trust deed is that it was a revocable trust that provided that “[W]hen John Arundel [the grantor] by the advice of Oliver Sent John wishes to have recovery of the minor, fees and advowsons . . . .” the trustees shall re-deed the property back “for John Arundel [the grantor] and his heirs male from the body of Isabel, daughter of Thomas de Molton, +knight to hold forever of the chief lords of the fee by services due with remainder, if John Arundel [the grantor] died without heirs male of the body of Isabel, to the heirs of body of John, son of John Arundel [the grantor]. . . .” (Cornwall Records Office AR/20/4).
https://kresenkernow.org/SOAP/detail/407a7dfd-c9fe-4d7d-a674-55593b79dcbe/?tH=%5B%22AR%7C20%7C4%22%5D
Both of these deeds provide that if there is a failure of heirs of John Arundel, Sr., then the first contingent beneficiary is Oliver St. John and his wife, Elizabeth de la Bere, daughter of Sir John de la Bere, and their eldest son, John St. John, for life and thereafter to the male heirs of Oliver St. John from the body of Elizabeth de la Bere, but if said male heirs fail the 2nd contingent beneficiary is Margaret, wife of Reginald Beuyle (Beville) and Ralph their son for their joint lives and thereafter Ralph Soor and the male heirs of his body but if his heirs fail the 3rd contingent beneficiary is John Colyn de Lannanta and his male heirs of the body of Rose, his wife, kinswoman of Sir. John Arundel, Sr.
There is an Arundel pedigree published in "Genealogical Collections Illustrating the History of Roman Catholic Families of England Based on the Lawson Manuscript, Part III", Edited by J. Jackson Howard and H. Seymour Hughes (1887-1892). On page 1 of this pedigree there is a Sir John Arundell who married 1st Elizabeth, daughter of Sir Oliver Carminowe, and married 2nd Isabella, daughter of Sir Thomas de Multon. Notes regarding Isabella say that there was a 1371 marriage settlement agreement, presumably at the time that John Arundell married Isabella de Multon, that matches the description of the above-mentioned deeds at the Cornwall Records Office.
The big question is - What is the marriage settlement agreement reason why Oliver St. John and his male issue from the body of Elizabeth de la Bere were named as the first remainder beneficiaries if the Arundel line died out, ahead of John Arundel, Sr.'s (the grantor's) daughter, Margaret, and his other more distant blood relatives?
I have a proposed answer that makes perfect sense to me, but I have no primary source direct evidence to prove it. What I propose is that Isabella, daughter of Sir Thomas de Multon/Moulton, first married Sir John de la Bere and from this marriage was born a daughter, Elizabeth de la Bere who married Oliver St. John. As a condition of Isabella remarrying to Sir John Arundel in 1371, a provision was made for Isabella's daughter from her first marriage and her male issue, ahead of John Arundel, Sr.'s daughter or more distant blood relatives.
I am hoping to find some documentary proof as to which Sir Thomas de Multon/Moulton had a daughter, Isabella, who married John Arundel and proof that his daughter, Isabella, was first married to Sir John de la Bere.
One interesting coincidence is that looking at a map of Glamorgan, Wales, the manor of Fonmon formerly owned by Oliver St. John and his wife, Elizabeth de la Bere, was very near to a hamlet called "Moulton". Does anybody know if there might be a relationship between the Sir Thomas Multon/Moulton who was the father of Isabella Multon/Moulton in the 14th Century and the name of this hamlet?
I really want this conversation to remain focused on the above mentioned question and proposed answer. It will not be helpful to this goal to discuss the Sir John de la Bere who married Agnes Turberville and had a daughter Elizabeth de la Bere who married John St. John of East Luccombe, Somerset, and had a connection to Weobley Castle in Wales.