*James 5th High Steward of Scotland
born about 1243 Scotland
died 1309

father:
*Alexander 4th High Steward of Scotland
born about 1214 Scotland
died 1283

mother:
*Jean MacAngus of Bute
born about 1218 Bute, Scotland

siblings:
*Elizabeth Stewart
*John Stewart (of Bonkyll) died 22 July 1298 Battle of Falkirk
*daughter of Alexander Steward

spouse:
*Cecilia of Dunbar
born about <1270> Scotland (one source says Ulster, Ireland)
died about 1320 Scotland
or
*Egidia de Burgh
born 1263 Ulster, Ireland

children:
Andrew Steward
*Walter 6th High Steward of Scotland born 1293 Dundonald, Kyle, Ayrshire, Scotland
died 9 April 1326 Bathgate Castle, Bathgate, West-Lothian, Scotland
John Stewart died 14 October 1318 Dundalk
James Stewart of Durrisdeer
Egidia Stewart born about 1296

biographical and/or anecdotal:

notes or source:
LDS
ancestry.com
"Biographical Encyclopedia of the Kings & Queens of Great Britain" by Mike Ashley
The sources are about evenly split between Cecilia and Egidia as the wife of James Steward.
Ashley (above) states Cecilia as the mother.
The pertinent question is why James & Walter would name their daughters Egidia.