CogSim, regarding two seated pilots the Chinese fire drills I posted can be tweaked to permit both of the seated pilots having had a chance to empty their bladders as needed during the interchange without having only one person at the controls for more than 20-30 seconds at a time. And when there were only two in the cockpit both would be seated at the controls. All they need to do is work through the procedure to see it can come together naturally.
With the bad wx zone so close I am sure they'd be all settled in for the duration of the crossing. Then they'd work out whatever was needed for emptying bladders when it was safe again.
Of course, conversation regarding radar here seems to indicate they might not have had the foggiest idea there was bad weather ahead before the fit hit the shan.