Sources

1) Source: Special Collections: Ancient Petitions "Ralph Bygot requests that the king order the justices to come to judgment in his case against Robert de Ferrers, his wife Margaret and John, son of Walter le Poure, regarding the manor of Bugbrooke."Dated: c1330. Reference: SC 8/181/9033 (Data from secondary evidence)
2) Source: Chancery: Inquisitions Post Mortem, Series I, Edward III "John de Bures...held for his life of the inheritance of John son and heir of Robert de Ferrers...He died on 21 December last. Katharine his daughter, wife of Giles de Bello Campo, aged 26 years and more, is his heir...He died on the feast of St. Thomas the Apostle last. Heir as above, aged 35 years and more...He died on 21 December last. Heir as above, aged 30 years and more...He died on 6 December...John son of Robert de Ferrar’, aged 19 years, is heir of the said Hawise de Ferres."Dated: December 1350. External Link
http://discovery.nationalarchives.gov.uk/details/r/C9777688. Reference: C 135/110/8 (Data from direct source)
3) Source: Varied - Secondary Source for Medieval Genealogy "However, a Close Rolls item dated 26 October 1349 reports that "Joan late the wife of Robert de Ferrariis, John de Ferrariis, John Uphay and Nicholas Poure, executors of the will of Robert de Ferrariis, came into Chancery on 19 October and there surrendered to the king that third part of the lands which Robert held of the lands which belonged to John de Beauchamp, tenant in chief." [Reference: Calendar of Close Rolls, 1349-1354 (1906): 139]. ". Reference: Douglas Richardson; "C.P. Correction: Death date of Sir Robert de Ferrers, de jure 3rd Lord Ferrers of Chartley [died 1349]" (Data from secondary evidence)
4) Source: Chancery: Inquisitions Post Mortem, Series I, Edward III "JOHN DE FERRARIIS, knight...He died on 31 March, 41 Edward III. Robert de Ferrariis, his son, aged 7 years and more, is his heir...Broghton. The manor, held in right of Elizabeth his wife, who survives. Elizabeth holds it for life as jointly enfeoffed with one Fulk Lestrange, her former husband, deceased, the reversion belonging to the heirs of John Lestrange, father of Fulk. The manor is not held of the king, but of whom else it is held the jurors know not.He died on 3 April last. Robert, son of the aforesaid John and Elizabeth, aged 7 years and more, is his heir." Date: 1367. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol12/pp105-118. Reference: C 135/193/13 (Data from direct source)