@No. 1: Not necessarily, they aren't direct descendants of the two brothers, as he claims to be, so that isn't a concrete example.
@No. 2 He ain't no Hidan. He doesn't crave pain for breakfast, lunch, dinner, and hourly snacks in between. With Kakazu gone, he would have n way of having his limbs reattached. And don't even mention Kabutorochimaru, he doesn't trust him at all, and will kill him the second he doesn't need him.