to be honest, I let the business about the wands go over my head! I too wondered how the sword got into the sorting hat as there was no mention of it leaving Gringotts Bank. Apparently a goblin put it in there? I don't remember for sure. I don't remember why Voldemort didn't kill Harry outright - I think it's cos the elder wand didn't work properly for him as he wasn't its rightful owner? I don't remember why Harry ended up being the owner of the elder wand. I was just grateful to see it go back to Dumbledore as it'd confused me!!!