I just tested the multiple envelopes and selected them all and could move all at the same time if they each had a node, but if I wanted to add a node it woukd only add one node, so you would have to add a node to each envelope.
If your delaing with a lot of envelopes say seven, this is not ideal at all.
It would be great if you could assign the same envelope to multiple parameters and then be able to scale each one within a range.