Sources

1) Source: Court of Common Pleas: Plea Rolls In Easter term 1342 John le Walshe, of Great Sherston, Wiltshire sued Alice, widow of Stephen de Segrave, in the Court of Common Pleas in a Leicestershire plea regarding a messuage; John son and heir of Stephen de Segrave was called to warranty.. Reference: CP40/330: Chief Justice's roll, 16 Edw III, Easter term (Data from direct source)
2) Source: The Mowbray Estate "John Germy; and Sir William Giffard and John de Segrave, son and heir of Sir Stephen de Segrave. Sat. after Epiphany, 6 Edw. IIIJohn has granted to William and John all the manors, vills, lands, holdings, hundreds, rents, services, knights' fees and advowsons which he had by grant and lease of his dear lord Sir Thomas earl of Norfolk, marshal of England, in the counties of Leicester, Derby, Surrey and Oxford, to hold of John Germy until the full age of the said John de Segrave.". External Link
http://discovery.nationalarchives.gov.uk/details/r/10d0fb06-0693-47b1-aaa5-55128bf7c157. Reference: BCM/D/5/1/4 (Data from direct source)
3) Source: The Mowbray Estate "John lord of Segrave; and Sir Stephen his son and heir and Alice, Stephen's wife. Sun. before the Purification, 7 Edw. II". External Link
http://discovery.nationalarchives.gov.uk/details/r/5ac46998-c63a-4e54-bdb5-c84dcab3674b. Reference: BCM/D/5/1/8 (Data from secondary evidence)
4) Source: The Mowbray Estate "Whereas John de Segrave has granted to John de Moubray an annual rent of £300 from his lands in Leicestershire, and another of £200 from his lands in Huntingdonshire, and one of £100 from his lands in Warwickshire, by three charters, John de Moubray has granted that if John de Segrave enfeoffs John son of John de Moubray and Elizabeth his wife of £100 of land and rent for Elizabeth's life, and the same to them for their joint lives, the charters granting the rents of £600 a year will be void." Agreement of marriage terms for his daughter Elizabeth.. External Link
http://discovery.nationalarchives.gov.uk/details/r/ea0f9c6a-6581-4a64-bf60-cc1361a1a03b. Reference: BCM/D/1/1/13 (Data from direct source)
5) Source: Chancery: Inquisitions Post Mortem, Series I, Henry IV "Thomas Moubray (Mowbray), earl Marshal...John Moubray, his brother and heir...He held the manors of Bosham and Stoughton in fee tail by the grant of Edward II to Thomas de Brotherton, his brother, of the lands of Roger le Bygod, sometime earl of Norfolk and Marshal [CChR 1300–26, pp.205–6]. They descended to Margaret duchess of Norfolk as daughter and heir of Thomas, from her to Thomas de Moubray, duke of Norfolk, as son of Elizabeth, daughter of Margaret, and so to Thomas as son of Thomas Moubray, and now to John Moubray as brother and heir...to William de Brewosa, senior, with remainder to John de Moubray and Aline his wife and their heirs. From them they descended to John their son, John his son, to Thomas duke of Norfolk, his son and heir, to Thomas the Earl Marshal, and now to John his brother...7 messuages and 10 bovates in Epworth, Haxey, and Owston in the Isle of Axholme, which John Lord Moubray, son of John, son of Roger"Dated: 1407. External Link
https://www.british-history.ac.uk/inquis-post-mortem/vol19/pp101-120. Reference: C 137/62/76 (Data from direct source)