Why do Haurchefant, Estinien and Yugiri have Hyuran last name?

[Alice_89th]

Greystone is the last name of all Ishgardian bastards (which means it is also the "true" last name of Hilda and Aymeric).

Aymeric his full name is confirmed as Aymeric de Borel in the MSQ of 3.3. At the very least, that is how he introduces himself to Hraesvelgr.