Again, here's the link to Vigenere. Last person need not encode merely say, so if you're new-ish or uncomfortable with it, there are only 7 of us.

Anyway mine is AfcupDbqsnpttn, let's knock 'em out since we only have a week. Even if we do get a double up, which is about 4 in 6 if someone is lying, which they may not be, we'll still need to figure out who and if we don't we'll not have long to find a new culprit.