Jeremy was a Hunter, more like Buffy's Slayer thing than what you guys are. For every vampire he killed, a tattoo on his body grew, the Mark. The Mark was part of the map to the Cure. Kill an Original, you kill their bloodline, tens of thousands of vampires dead with one stake. Boom, one complete Mark.
Finn was always a bit weird. Even a little bit creepy. I'm not going to pretend his death affected me as much as Kol's, but he was still my brother. An Original can only be killed by a stake made from a specific tree, the one used in the spell of our creation. So there's only one stake like that left. My mother, charming as ever, did a spell to link us together, what happened to one, happened to all of us. So Team Gilbert got Finn alone and staked him, hoping to kill the lot of us. Fortunately the spell had been broken. That was when we all found out that the bloodline dies with an Original.
I know what Klaus is like. Believe me, I know better than anyone, no one has suffered more than I have at his hands. A thousand years by his side, he has killed so many of my lovers, shoved a dagger in my heart repeatedly, stole a century from me like it was nothing and comments now that he wishes he had the daggers again so he can put us on a forced time out for a few decades. But he's my brother. And a thousand years by his side, I can't walk away from him. I love him as much as I hate him. Even now, a couple of days ago he decided he's disowned the lot of us now.
I'm not a good person. I'm also not an evil monster. I may not regret killing Elena, but I regret a hell of a lot over my long life. There is a lot I wish I could take back. I'm also a massive brat and incredibly selfish at times and so stubborn. But back home, and from some people here, they want to shove us all into neat boxes. Elena's Good and I'm Bad. And it's no where near that simple. We both started out as innocent kids and got screwed over a lot. We've both killed a lot. I don't regret killing her, she's flat out told me here that she doesn't regret killing Kol or his bloodline and she'd do it again. So if I'm a selfish monster, she is just as bad, if not worse than I am.