We do 1 group on each, group of rogues on TZ and a group of misc melee, zerkers and monks on VZ, then have wizards pop in on VZ if they fall behind. You can save on some deaths by having people meleeing vz back out when he splits.
Other then that just balance them down while the rest of the raid takes care of adds.
At 10%, get people off the brothers and help finish adds, once the last add dies you win.
Having a designated rezzer / rez area helps too to get people back up quickly.