Wow sounds like you are going through a lot right now. Sounds like things need to get out in the open between you all - it is the only way you can get past all this. I don't think it was wrong for you to tell sister #2 whats been going on and what is being said. I know if a family member was saying bad things about me behind my back I'd want to know. Yes I'm sure sister #2's feels are hurt - things like that always do. But she can't deal with a situation she does not know about.

No I do not think you should have kept everything in - for 2 reasons. One it would eat you from the inside out and that is not healthy for you. Two, Sister #1 needs to know that her actions and words have consequences.

Maybe all three of you need to get together and tell each other how you feel. If sister #1 behaves as you fear she will, that is her choice. But she has to learn that you both have choices also and will not suffer because of her behaviour.

Follow your heart and remember they will always be your sisters, but at the same time stand up for what you believe to be the right thing.

I wish you all the best