Possible spoilers...
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I looked at some raws and I think that Lorkan faces a contract onto Brian while he's on a mission to another town, and asleep and recovering. Brian doesn't know this and Sol senses it when he hugs him. So now Brian has an eternal contract with both brothers—one with Sol, which was by mutual consent and is an agreement between partners/lovers, and one with Lorkan, which is more like slave-master relationship.
It explains the present, where Sol was looking for Ian and Lorkan had him under his thumb the whole time. And Sol didn't manage to find Ian until he had grown up, and was living in a nation that's hostile to magic users, so little orphan Ian grows up ashamed of himself and is trauma bonded to Lorkan. If Ian had been born in Archaia and had grown up under Sol's watch, things would be different and he wouldn't be so emotionally damaged and wary. But we wouldn't have all the drama and conflict of this story ha ha.