Yeah, I understood it as all the souls being inside Father, too. But I didn't think about him making all of them - Ed & co - into philosophers' stones, same as he made HH. That would make sense as to why Father needed them. But why would he be able to use HH then, if he's already "full" of the Xerxes souls? (can you be "full"?) Weird, I hadn't thought about that.