depending on how long you want the one shot to run, you might consider loosening up the magic item selection a bit. It would need to be players who are familiar enough with the system that the items didn't over whelm them, but getting a staff of defense, somewhat better armor, etc, would also help players round out the party defenses. (and since they have a higher level master in the background, it could be them "borrowing" his selection of items.