When Harry said because they took Maggie from him, Eb said "her too". It was almost like an afterthought to me like his hate for them was deeper than Maggie. It came before her.
Eb is over 300 years old, and Maggie was around 100 when Harry was born. So Eb went 200 years without other children? I was thinking it may have been his wife who was taken from him, but now I'm wondering if Eb had a wife, and children before meeting Maggie's mother, and that's why he kept her at arms length. He'd already lost one family, and when he had her, he raised her differently.
I think the way he talked about Harry and Maggie, and how Harry was putting a target on her back, and he was beyond livid about it. He was very very upset. Then his talk about the vampires reached the point of being over the top. Even when facing Outsiders he took the time to be upset about the vampires.. This has to be more than losing some friends to vampires. The only thing that makes sense is he had a family before Maggie, and her mother.
My theory is that Eb had a wife, and kids, and they were all slaughtered by vampires, maybe even turning them into vamps that Eb later destroyed.
What do you think? What do you think could have driven Eb to the point of murderous rage finding out Thomas was his grandchild? I can't think of anything else besides losing a wife, a child or more.