OOooohhh... My mother did that to me once when I was 17. I KNEW my brother was the guilty party, and I was convinced she did also, and just wanted to pick a fight. Anyways I LEFT with friends and didn't come home for a week.
We had issues...
I don't think punishing all for the sins of one is fair. Since the guilty party knows he's in for it anyways, what motivation does he have to "fess up? Why not make his pain-in-the-butt sister/brother suffer as well?
I guess I don't have much to offer for dealing with lying. It hasn't been an issue for dd - it's just not her personality. My 4 year old ds I think may be another story... I guess the only thing I can think of so far is a) not let them lie (i.e. "What did you use to cut your sandals?") and b) make sure they feel safe telling me the truth. However, I know some kids will lie no matter what you do (my brother was like this).
This doesn't help much, I know - I will be watching for replies from the more experienced moms.