Thomas de Lancaster - parents - disconnect from Sir Robert Lawrence?

Notes in profile:

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Thomas de Lancaster was born say 1225. Thomas died circa 1292.

About 1247 the abbot and convent of Furness granted a toft to Thomas son of Roger de Lancaster in perpetual farm at 5s. rent; there was an oven on it.1 The estimated birth date of Thomas de Lancaster is based on this transaction. It would appear that Thomas may have been the eldest son of Roger de Lancaster, not a younger son as stated in The parentage of William de Lancaster, lord of Kendal by Washington.2 Thomas appears to have died circa 1292, about the same time as Roger de Lancaster or perhaps even before his father which may account for the lack of mention of Thomas as a heir of Roger. Also, was Thomas perhaps an illegitimate son of Roger, born before his marriage to Philippa de Bolebec?

http://www.lawrencefamhis.com/ashton-o/p230.htm#i5739

Thomas de Lancaster had two sons, John de Lancaster, the heir, who had no issue, and Lawrence de Lancaster, the eventual heir.

From The de Lancaster family of Rainhill, Lancashire

A Thomas de Lancaster, son of Roger, who is the ancestor of the Lawrences of Ashton, certainly had a son named John de Lancaster, but he seems to have died without heir, leaving his brother Lawrence to take over the estates of this family, in the countryside around Lancaster. I do not know of any involvement by this family in southern Lancashire in this period.