FMG doesn't bother with mere barons, and has trouble tracing the various lineages. He's definite that the sons of Roger FitzCorbet were 1) William (-after 1166), 2) Everard, and (maybe) 3) Simon, although the possibility is noted that Simon may be son of Everard and *grandson* of Roger.
Robert ((-after 1124, Roger's brother) is noted with two wives, neither one known, and child 1) Sybil ([1090/95]-after 1157) (mistress of Henry I, like every female the King got anywhere near), then m. Herbert FitzHerbert; 2) Robert (II) (-after Jul 1141), who may have hiked up to Cumberland and so to Scotland in service to King David (previously Earl of Cumberland); 3) Alice, m. William Boterel. Robert jr did not inherit, either because he died or because he could not be bothered to schlep back to Shropshire.
Next Corbets reported are brothers Roger (II) (-[1162]), m. Hawise somebody, and Simon (-before [1162], wife unknown). Roger is thought to have died childless; Simon managed a son Robert III but may have predeceased his brother - at all events Simon's son Robert (III) inherited and kept the line going.
Robert III (before [1158]-[22 Jul 1219/17 Oct 1222]) m. (unknown) and had 4 children:
1) Thomas (-before 2 Nov 1274), who m. Isabel de Valletort (widow of Alan de Dunstanville, daughter of Roger de Vautort of Harberton, Devon - no children from first marriage)
2) Hugh
3) Robert (IV)
4) Mary/Margaret (-after 15 Apr 1231), m. our old friend Gwenwynwyn of Powys - most sources call her Margaret, so I don't know where "Mary" comes from.
Getting back to Thomas (I), he and Isabel had three (documented) children: 1) Piers I (alias Peter, (-1300 before 10 Aug)), specifically named as "of Caus"; 2) Alice, m. Robert de Stafford (which eventually gave Caus Castle to the Staffords), 3) Emma, m. Brian de Brampton.
Piers/Peter m. 1) Joan de Mortimer, 2) Alice unknown.
Two sons by Joan: 1) Thomas (II) (-before 11 Nov 1295), heir, m. Joan Plugenet but died childless; 2) Piers/Peter (II) of whom more in a bit.
Two (known) children by Alice: 3) John (25 Mar 1298-before 1347), 4) Alice m. John de Harcourt.
Piers II ([1269/70]-before 29 Jan 1322) married Beatrice de Beauchamp (-before Oct 1347), and named a John Corbet as heir to the manor of Bynweston, but it isn't clear whether this is his son, his half-brother, or some other John Corbet. What IS known is that as of October 1347 Caus Castle was in Stafford hands and the Corbet barony of Caus was extinct.
There's a ragged tag-end at the bottom:
The chronology suggests that Thomas Corbet, shown below, was the son of either Hugh Corbet or Robert [IV] Corbet who are shown above or was descended from an earlier younger branch of the family.
1. THOMAS Corbet (-before 18 Jul 1247). A writ dated 18 Jul "31 Hen III", after the death of "Thomas Corbet of Tasselegh" names "Roger his son aged 25 is his heir" and "Bromleg manor" in Staffordshire[2838]. m ---. The name of Thomas’s wife is not known. Thomas & his wife had one child:
a) ROGER Corbet ([1221/22]-before 7 May 1259). A writ dated 18 Jul "31 Hen III", after the death of "Thomas Corbet of Tasselegh" names "Roger his son aged 25 is his heir" and "Bromleg manor" in Staffordshire[2839]. A writ dated 7 May "43 Hen III", after the death of "Roger Corbet" names "his heir…Thomas…aged 11 on the eve of the Exaltation of the Cross next" and Bromley manor in Staffordshire[2840]. m ---. The name of Roger’s wife is not known. Roger & his wife had one child:
i) THOMAS Corbet (13 Sep 1248-before 10 May 1300). A writ dated 7 May "43 Hen III", after the death of "Roger Corbet" names "his heir…Thomas…aged 11 on the eve of the Exaltation of the Cross next" and Bromley manor in Staffordshire[2841]. Inquisitions dated "10 May 28 Edw I", following the death of "Thomas Corbet of Tasseleye", name “Roger Corbet his son, aged 27 at the feast of St. Michael last, is his next heir”[2842]. m ---. The name of Thomas’s wife is not known. Thomas & his wife had one child:
(1) ROGER Corbet ([1272/73]-). Inquisitions dated "10 May 28 Edw I", following the death of "Thomas Corbet of Tasseleye", name “Roger Corbet his son, aged 27 at the feast of St. Michael last, is his next heir”[2843].