I am probably one of the few that doesn't find it odd that he lives at home. He also might not have wanted his mother living alone- there are good sons that do care about their moms not living alone, and seeing that he has been a farrier for a good amount of time now and is established, it would make sense for him to stay there, and if him and Kelsey did get married, living there afterwards. Who knows, maybe this was a cause of frustration for Kelsey- perhaps she didn't want to move in with his Mumsy and he insisted. Perhaps this was a thorn in their relationship and she was tired of waiting for him to choose.
Still, he is a sick individual to murder her or have her murdered like that, no matter what the case. Self defense is one thing, but this isn't the case here. No excuse for what he did, and he was obviously planning this before Thanksgiving, which is just horrific to think about.