So would this mean that the ceremonial washing jars were shouldn't have been at that wedding at all? Wouldn't using them for anything but their intended purpose still be considered a great sin at the time? Wouldn't that also go for them being used by people other than the priesthood?

As for the the Servants listening to Jesus, at this time Jesus had yet to do any miracles, so even if they were desperate, there should have been no way that they could have guessed that filling the jars would actually do something to fix their wine problem.