Sir Robert of Biggleswade - Wrongly assigned parents of Robert de l'Isle?

Just looking at the trees it would seem to make sense if this Robert were the son of a Warin who was son of Robert 1195-1262 with brother Gerald 1248-1288.
The Warin de l'Isle he is currently assigned as son of doesn't match because the overview states that his father died while he was an infant before 7 December 1296 whereas the Warin that he is assigned as son of was hanged 1321/22.

Opinions sought.