with running backstays, if you're making quick, short (or no)-warning jibes, there should be one crew on each backstay winch. As soon as the boom comes away from the old "lazy" stay, tension it up, using the second crew on the other side as a sheet-tailer if necessary.
Then, it's a one-crew job to ease off the new leeward lazy stay.
The most critical thing is tensioning the "new" backstay, for obvious reasons.
Normally, at the start of a race (to windward), no one need be near the runners. If you're over early, then you have to change gears fast.