Curently he is the great uncle, but he might need to be moved a generation down to make him the uncle.
John "held the manor of Spitchwick in his demesne as of fee of Robert Ponnyngys, knight, of his manor of Stogursey in Somerset by knight service, annual value 10 marks."
John's heir was "Fulk Fitzwaryn son of Fulk, son of Fulk his brother"
In the Devon IPM for Fulk FitzWarin (1406 - 1420) it states: "John Fitzwaryn was seised in his demesne as of fee of the manor of Spitchwick and on his death it descended to Fulk son of Fulk Fitzwaryn, knight, a minor, as his heir, i.e. son of John's brother Fulk, and was taken into the king's hand, where it remains. The manor is held of Robert Ponynges, knight , of the manor of Stogursey by knight service."
John is not in Richardson's book Royal Ancestry.