Sources

1) Source: Chancery: Inquisitions Post Mortem, Series I, Henry III "Richard de Clare, earl of Gloucester and Hertford...to the said keepers, dated 8 July, the king has granted to Gilbert de Clare, son and heir of Richard de Clare sometime earl of Gloucester, all the fruits of this autumn, viz.—of the 47th year of his reign, of all the lands, &c. which were his father's, for which he is to account at the king's exchequer, saving to William de Valencia, the king's brother,"Dated: 1262 Evidences that Richard is father of Gilbert.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp149-165. Reference: C 132/27/5 (Data from direct source)
2) Source: Exchequer: Treasury of Receipt: Ancient Deeds, Series A "Demise by Thomas de Clare, brother of Gilbert de Clare, earl of Gloucester and Hereford, to Dame Rosamund, late the wife of Sir Geoffrey Marmyun, of land, etc. of the manor of Chakenden belonging to him by reason of his wardship of John son and heir of William Marmyun". Date: 31 March 1266. External Link
https://discovery.nationalarchives.gov.uk/details/r/C4947943. Reference: E 40/9184 (Data from direct source)
3) Source: Chancery: Inquisitions Post Mortem, Series I, Henry III "Richard de Clare, earl of Gloucester and Hertford...to the said keepers, dated 8 July, the king has granted to Gilbert de Clare, son and heir of Richard de Clare sometime earl of Gloucester, all the fruits of this autumn, viz.—of the 47th year of his reign, of all the lands, &c. which were his father's, for which he is to account at the king's exchequer, saving to William de Valencia, the king's brother,"Dated: 1262. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp149-165. Reference: C 132/27/5 (Data from secondary evidence)
4) Source: English Baronies: a Study of Their Origin and Descent, 1086-1327. Reference: Pages 34-35: Clare (Questionable reliability of evidence)
5) Source: Chancery: Inquisitions Post Mortem, Series I, Edward I "Joan, late wife of Gilbert de Clare, sometime earl of Gloucester and Hertford, the king's daughter...Gilbert de Clare, aged 17 on 11 May last, is next heir of the said earl and Joan...She died 19 April, 35 Edw. I...wherein the said Joan was not conjoined, for Alice de la March, sometime the wife of the said Gilbert, held (it) by his demise...Maud de Clare, sometime countess of Gloucester, in her widowhood procured...the same descended to the heirs of the said Gilbert and Joan by the said Jordan’s death, as heirs of the said Maud"Dated: 1307 Tentative evidence that Maud is mother of Gilbert de Clare.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol4/pp311-331. Reference: C 133/128/1, C 133/129/1, C 133/130/1 (Data from secondary evidence)
6) Source: Chancery: Inquisitions Post Mortem, Series I, Henry III "Richard de Clare, earl of Gloucester and Hertford...to the said keepers, dated 8 July, the king has granted to Gilbert de Clare, son and heir of Richard de Clare sometime earl of Gloucester, all the fruits of this autumn, viz.—of the 47th year of his reign, of all the lands, &c. which were his father's, for which he is to account at the king's exchequer, saving to William de Valencia, the king's brother,"Dated: 1262 Evidence that Maud is mother of Gilbert.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp149-165. Reference: C 132/27/5 (Data from direct source)
7) Source: Chancery: Inquisitions Post Mortem, Series I, Edward II "Gilbert de Clare, sometime earl of Gloucester and Hertford...Maud, late the wife of the said Gilbert [Badlesmere], in the king’s court at Westminster claims a third part in dower against Bartholomew de Badelesmere, who vouches to warrant Hugh le Despenser, the younger, and Eleanor his wife, Hugh de Audeleye and Margaret his wife, and Roger Dammari and Elizabeth his wife, sisters and heirs of the said earl"Date: 1318 Evidences that Gilbert de Clare is father of Eleanor, Margaret and Elizabeth de Clare.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol6/pp110-129. Reference: C 134/63/10 (Data from direct source)
8) Source: Special Collections: Ancient Petitions "Hugh de Audele and Margaret his wife state that they entered the manor of Thaxted in Essex as of the right and inheritance of Margaret, and have long been peacefully seised of it, Margaret, widow of Bartholomew [de Badlesmere], is suing a writ to expel them from this manor, claiming a right in it although she has none... People mentioned: Hugh de Audele and Margaret his wife state that they entered the manor of Thaxted in Essex as of the right and inheritance of Margaret, and have long been peacefully seised of it, Margaret, widow of Bartholomew [de Badlesmere], is suing... People mentioned:Gilbert de Clare, Earl of Gloucester, father of Margaret de Audele; Thomas [of Lancaster], Earl of Lancaster; Margaret [de Badlesmere], widow of Bartholomew de Badlesmere; Bartholomew [de Badlesmere]." Date: c1327. External Link
https://discovery.nationalarchives.gov.uk/details/r/C9061707. Reference: SC 8/31/1513 (Data from direct source)
9) Source: Special Collections: Ancient Petitions "Petitioners: Rose de Moubray (Mowbray), widow of Roger de Mowbray."Dated: 1299. External Link
http://discovery.nationalarchives.gov.uk/details/r/C9517521. Reference: SC 8/272/13574 (Questionable reliability of evidence)
10) Source: Special Collections: Ancient Petitions "Margaret, widow of Bartholomew de Batelesmere, and one of the sisters and heirs of Richard de Clare, states that while she was in the king's prison, Robert de Welles, the husband of Maud, the younger sister, with the aid and maintenance of Hugh le Despenser, had the lands of the inheritance assessed and took Maud's share, both in England and in Ireland, although Margaret did not assent to this division or take anything. She requests that the division might be made again, according to the assessments returned in Chancery, and that she might have the choice of her share, as she is the elder sister."Dated: 1327. External Link
http://discovery.nationalarchives.gov.uk/details/r/C9061756. Reference: SC 8/32/1559 (Data from secondary evidence)