Joe's loyalty to Duncan over the Watchers makes it impossible to place him anywhere else.

Methos as Salazar...that is brilliant! Where would I find those stories?

Amanda was the hard one for me, she's all over the map with her personality and doesn't completely fit into any of the houses. Although, I keep thinking about how in Lady and the Tiger she took Zachary's head while Duncan fought him. That screams Slytherin.