Sources

1) Source: Chancery: Inquisitions Post Mortem, Series I, Richard II "Margaret late the wife of Roger de Claryndon, knight...Thomas de Roche, son of John de la Roche, knight, son of Robert de la Roche, knight, son of Joan de la Roche, one of the sisters of William de la Roche, father of the said Mariot...Thomas a minor"Dated: 1391. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol17/pp65-71. Reference: C 136/74/6 (Data from direct source)
2) Source: Chancery: Inquisitions Post Mortem, Series I, Richard II "Margaret, late the wife of Roger de Claryndon (Clarendon), knight...William de la Roche, her grandfather, late lord of the said manors, had four sisters, Joan, Alice, Margaret and Lucy. Joan was married to David de la Roche of Landecomb, and they begat Robert de la Roche, knight, who begat John de la Roche, knight, who begat Thomas de la Roche, who is kinsman and one of the heirs of the said Margaret. He is 11 years of age and more."Dated: 1382. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol15/pp290-307. Reference: C 136/25/3 (Data from direct source)