Please note that I'm not a native English speaker and I can't grasp 100% of what is said on the screen, so the answer to this question could be very trivial if it turns out that I've just missed an important sentence.
Even before the ritual is performed the original are all "linked" so the death of one is the death of all. So what's the point of having a ritual if the only thing to do was for Finn to kill himself, in order to kill all other originals AND all other vampires in the world (as explained later the death of a vampire wipes out all the related line)?
Also, at the beginning of "The Murder of One" Finn tells Klaus that he and their mother haven't given up, yet, even if the ritual failed. But, again, he only needed to kill himself (or allow the mother to do so) to kill all the others since they are all still linked at that point.
So what were they trying to achieve with the ritual?