I'm fine with your character, however he wouldn't be living in the Nemisis' cabin, he would be in Athena's cabin. Also Lamia's weren't known to keep the children they stole alive, they weren't the smartest, but they were ravenous and vicious creatures that would snap the necks of their prey so they could eat; when some children died young or went missing it was said to be the work of a Lamia.