Couple of points to consider.
1. Why are they so weak? If I read your post correctly, they have plenty of stores, so starvation is not this issue. Did you check for mites? Unless you understand what weaken them and rectify it. They will most likely fail.
2. If your still having cold weather, a couple hundred bees will have a hard time keeping the temperature up to raise brood. You might consider providing supplimental heat, such a reptile heater as recommended by Finman, or a light bulb (my cheaper alternative). I have successfully saved late season swarms that where down to a handful of bees with 2 - 7watt nite lights placed on the bottom board. The bees rasied brood in the bottom of the frames right over the light bulbs.