I know about your rift, and I know that keeping quiet and being supportive is the only way now. That's exactly what I'd be doing, but still.......that's not what I'd be thinking inside.
Also, I know I would have handled your sil 100% statement, just like you did. But inside I would have been thinking that there's no way in HE!! that I'd be able to be 100% supportive. Again, I'd just have to take that one day by day.
You'll do fine - you always do. You have such a good attitude about all of this. You can't change a thing that they may do, so just try to be as supportive as you can and go with the flow - which you are already doing.
I like Diane's signature line, I can't remember exactly, but it's something like, live for today and tomorrow will take care of itself. BUT, I'm a supreme planner and so I would still be thinking
OMG! What are you people thinking!!! 