I was doing the new patch quests and while in the Heart Chamber Wrathion and Ebonhorn had a quick exchange of dialogue (which I didn't screen shot) where Wrathion says that Ebon is his only/last brother. What about Sabellian? https://wow.gamepedia.com/Sabellian DRAGON PARTY.
Fun fact: While googling the dragon I came across "Sabellianism is the belief that the Father, Son, and Holy Spirit are three different modes or aspects of God, as opposed to a Trinitarian view of three distinct persons within the Godhead." 3 aspects of a god... 3 dragons... I'm grasping for straws, but thought it was worth mentioning.