Sources

1) Source: Chancery: Inquisitions Post Mortem, Series I, Henry III "William Maudut alias Mauduyt, Mauduth, earl of Warwick...He had no heir of his body; William de Bello Campo the younger, son of his sister Isabel deceased who was married to William de Bello Campo the elder, age variously stated as 26 and more, and 30 and more, is his heir"Dated: 1268 Evidences that William is father of William.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp208-217. Reference: C 132/35/13 (Data from direct source)
2) Source: Exchequer: King's Remembrancer: Ancient Deeds, Series D "Agreement between Sir William de Bello Campo, son of Walter de Bello Campo, sheriff of Worcester, and Sir Thomas the abbot, and the convent, of Evesham". Dated c1242. External Link
https://discovery.nationalarchives.gov.uk/details/r/C5514014. Reference: E 210/134 (Data from direct source)
3) Source: Testamenta Vetusta: Being Illustrations from Wills, of Manners, Customs Etc. as Well as of the Descents and Possessions of Many Distinguished Families from Henry II. to Queen Elizabeth "anno 1268... to Walter, my son... of Isabel his mother... to Joane, my daughter... to Isabel, my daughter... to Sibill, my daughter... to Sarah, my daughter... to William, my eldest son... to my daughter the Countess, his wife...". Reference: Page 50; William de Beauchamp (Data from secondary evidence)
4) Source: English Baronies: a Study of Their Origin and Descent, 1086-1327. Reference: Pages 93-94: Warwick (Questionable reliability of evidence)
5) Source: Chancery: Inquisitions Post Mortem, Series I, Henry III "William Maudut alias Mauduyt, Mauduth, earl of Warwick...He had no heir of his body; William de Bello Campo the younger, son of his sister Isabel deceased who was married to William de Bello Campo the elder, age variously stated as 26 and more, and 30 and more, is his heir"Dated: 1268. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp208-217. Reference: C 132/35/13
6) Source: Chancery: Inquisitions Post Mortem, Series I, Henry III "William Maudut alias Mauduyt, Mauduth, earl of Warwick...He had no heir of his body; William de Bello Campo the younger, son of his sister Isabel deceased who was married to William de Bello Campo the elder, age variously stated as 26 and more, and 30 and more, is his heir"Dated: 1268 Evidences that Isabel is mother of William.. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp208-217. Reference: C 132/35/13 (Data from direct source)
7) Source: The History of Parliament . External Link
http://www.historyofparliamentonline.org/volume/1386-1421/member/beauchamp-sir-william-1421. Reference: Beauchamp, Sir William (d.c.1421), of Powick, Worcs. and Alcester, Warws. (Unreliable evidence or estimated data)
8) Source: King's Remembrancer: Accounts Various "Funeral expenses of Walter de Bello Campo."Dated: c1303. External Link
http://discovery.nationalarchives.gov.uk/details/r/C4520465. Reference: E 101/507/4 (Data from secondary evidence)
9) Source: Chancery: Inquisitions Post Mortem, Series I, Edward I "ISABEL LATE THE WIFE OF HUGH LE DESPENSER... Her daughter Maud, now the wife of Henry de Langastre, aged 24, is her next heir. Charter of William de Bello Campo, earl of Warwick, granting to Sir Patrick de Cadurcis, with Isabel his daughter in free marriage," Date: 1306. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol4/pp229-238. Reference: C 133/121/11 (Data from secondary evidence)
10) Source: Chancery: Inquisitions Post Mortem, Series I, Edward I "William de Bello Campo (Beauchamp), earl of Warwick...Guy de Warr(ewick) his son, aged 24 and more, is his next heir...Schefeld. A tenement in the manor called ‘le Dichall’ held of the dower of Maud his wife, of the lands &c. which were of Gerard de Furnivall her first husband; which tenement after her death ought to revert to Thomas de Furnivall, now lord of Hallumschire, as kinsman and heir of the said Gerard."Dated: June 1298. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol3/pp375-387. Reference: C 133/86/1 (Data from secondary evidence)