Tractor Driver - 121.5 won't alert anyone any more, the COSPAS/SARSAT monitoring of that and 243.0 has finished so the answer is either your 156.8 alert to the SBV or a personal 406Mhz beacon.
As to the second scenario - if I pitched up on scene and only had the one strong signal (whether from the raft or ADELT) I would have to go there first but the chances that anyone is still with the aircraft are slim and if there are people in the rafts, they are at least safe from the environment. If the crew are in the rafts they probably wouldn't activate their beacons, if they are in the water they would but these would be supressed by the raft/ADELT. Any pax with WWPLBs in the rafts might suppress the ELTs and give a poor homing signal and any who are in the water drifting away would be very low down the pecking order if they had smart beacons.
In terms of rescuing priority it has to be the guys in the water with the WWPLBs since they are pax and have the least training compared to the crew and probably inferior safety equipment. If you give them smart PLBS they could be suppressed by all the others and you wouldn't know they were there until you had got the guys from the rafts (who are in less danger) out first.
The potential confusion with multiple beacons at least gives you an idea of what you are faced with ie possibly 21 pax in the water whereas one strong signal might give you an easier homing but far less information about how you need to proceed.
The aircraft beacon should be 406 and it should have encoded GPS so homing is almost unneccessary (they transmit every 50 secs or so) - the crew should be similarly equipped.
Even if it is foggy, we have more than just homers to find pax in the water - the FLIR will help and at night, so will NVG since most lifejackets have a light on which will stand out like a dog's whatsits on goggles.
Overall, since the priority must be to rescue pax from the water before pax from a raft, you must select a system that doesn't mask their individual signals if you want to give them the best chance.
It would probably take nearly an hour to winch 21 people out of the water, especially at night in fog, even if some of them are in rafts and the winchman would be knackered by the time you got halfway through. Any further searching for those who might have continued to drift away whilst you rescued the raftees first would mean longer exposure times and decreased chances of survival.