From what I've heard, Skype is particularly hard to classify. Like bittorrent, its clients don't always use the same port, and it opens whatever it wants via UPnP. However you can set a specific port inside of the skype client.
With only 10 people it wouldn't be hard to ensure that they were all set to use a small range of ports, and then manually set those ports to make it into the proper queue. That doesn't solve the problem of the outgoing traffic, which will still be to a random client port, but it may at least help.