Clearly a mix up and the early supposed GILBERT family from a GedCom import for much later sourced descendants. From a quick look, the tree for that time is similar to others on-line such as http://knight-france.com/geneal/names/1330.htm
none of which appear to have any primary sources. If the ancestors are as claimed, they do not appear to me to agree with a Gilbert tree in a Visitation done in 1563 when the ancestors died without issue! Since recently joining, I had not checked the 3 GYLBERTS here on WikiTree. I prefer to use the modern spelling GILBERT in the One-name Study for all, with the contemporary spellings found in primary sources given as AKAs for the early profiles. I will look to sort these entries out in due course once I have seen if they can be resolved.