Hi Nootellix,
Thank you for your question! I'm glad you are so interested in the side characters and all the confusing twists of Ilyon's scattered memories.
Spoilers
Krey(elf) is actually Serci's(elf) brother. He's Ilyon's uncle who took him in after Serci and Ilyon's human father Cayden were killed by the Council, for their forbidden union. Krey's own wife and child died in childbirth, so Krey and Serci tried to save Ilyon by pretending he was Krey's child. This is why Krey bitter/neglectful towards Ilyon. To him, his unnatural existence of being a half elf, half human cost him everyone and was no replacement for his deceased wife and son. In one of the alternate reality, Caylis's cousin is still alive and he looks similair to Ilyon but with purple hair like Serci and Krey. Sorry it's been a long time since I looked at this story!