Old batches so not exist any more. Joseph wouldn't know the difference any way. Yes, it is essential that Joseph does not know about the old batch. 

He is going to be presented with, basically, Alexi's soul, and aside from sharing and possibly boosting how Erik and Alexi feels about slavery and the like, it will be up to Erik how the positive emotions affect him. Since Alexi is all about free will, it will be entirely Erik's choice.

No, since Erik is the only one taking the potion, he will be the only one affected.

Not for nothing. It's that fire of resistance that makes him so appealing and the right person for the thing Alexi's trying to do. His suffering will not only show Alexi that he's still up to the task, but will(One would hope) prove to Erik that not only can he resist, but that Alexi wants him to. Think of it like the first sign(Other than the lack of crushing negative emotions) that the thing taking place isn't meant to break him. I see it taking a few doses for that to sink in.

Indeed. He doesn't want to negotiate with Erik, or even support him behind the scenes. He wants to share. *Can't say more, will ruin surprise even more than it already is from all these questions :P*

Right again. It will take a few doses for Erik to even get an inkling as to what is happening to him.

~*~*~*~*~*~*~

*Nods* Neat Idea. Glad I can help out wif da back story. The humans would, since they are humans, not see the torture that way, which is why they got so mad. Because the thing feeding on them looks like humans, they assigned human morals to them. 

Oh, and I forget this discussion, but I wanna put it down if we forgot, to give another option later on, vampires are made, not born. . .I think we already agreed on that, but I seem to have forgotten. . . .