In the AOA, Sabretooth first met Wildchild in Alcatraz, Kyle had been confined there for attacking Holocaust, and had eaten his last three cellmates, so when Holocaust caught Creed trying to protect some human kids from Apocalypse's Infinites
he had him thrown in with Kyle, hoping he'd be killed...They fought for three days and nights until Kyle accepted Sabretooth as the "Alpha Male" then they broke out and joined the X-Men...(Sabretooth being
kind, now that's bizarre!)
As far as I know they aren't related at all, Victor said it was the first time he'd laid eyes on Kyle. {Age of Apocalypse One-Shot #1}
It's hard to tell, in X-Factor they were really making Kyle out to be Sabey Jr., it was kinda hinted in Marvel Comics Presents, but the Alpha editors said he was definately not Creed's son and Weapon X never seemed to mention it, as far as I know. One of the people at the Wildchild "Child of Darkness" message board said she'd read somewhere about a another Creed (not Graydon)...
It's all up to the writer's whims..