I don't think that Stefan is adopted. I think that Damon and Stefan are normal brothers, because Katherine had a family too and she had siblings (which were murdered by Klaus just as the rest of the family). And Damon is just a normal person/vampire whatever, Stefan is the doppelgänger and yeah. My opinion :)
as i understood, it's like this:
klaus is half vampire and half werewolf. vampires can't have babies, that's right, but werewolves can. so when he broke the curse, he could procreate again and so hayley is pregnant with his child now.
the other side is where supernatural creatures get after they died and when Silas takes the cure he becomes a warlock again, which he was before turning into a vampire. so he's still a supernatural creature and would end on the other side.
exactly my thoughts. rebekah wants it for herself, stefan and damon want it for elena but they actually need it for silas. i was very disappointed here, because they are all so selfish -.- silas will just kill them all if anybody besides himself takes the cure.
if the cure is really a cure - which i doubt after reading all the posts here - and Silas took it, i think it would turn him back into a warlock, because thats what he was before turning into a vampire. and because witches are supernatural they get to the other side after dying which will separate silas from his lover, who was a human. i guess this is the reason why silas wants to destroy the other side, it is the only way for him to be with his lover after dying.
I thought about this too, it is very weird, yeah. I think it's like what happend to Elijah when he got staked with a normal stake, he was 'dead' for a few hours and then resurrected. That's probably what would happen to Klaus if he got ripped out his heart or his head off. I guess it's the same with the other originals, due to the fact that they just can be killed with the white oake stake.