robin,
give them feed until you know what's going on, and don't stop until you do....
how old is your queen, if you know?
what 'genetics' of bees/queen are you keeping?
how many frames do you think the bees covered just from opening it up?
stay to two deeps, don't mess with pulling boxes, bees move up in winter months to stores in the top deep, they will not go back down to the bottom deep. if they are out or close to being out of stores in the top deep, add sugar bricks, or some type of fondant. don't pull frames until it is warm enough and don't pull frames to look for the queen. if the queen is absent, you will not be able to 'strengthen' them. if she is present, FEED and don't stop feeding. sugar bricks, or sugar supplement thrown in on top of the frames.
at this point you don't know if the queen is missing, so i would feed them and don't stop until you know. sometimes bees can overwinter and come out in smaller clusters! if the queen is gone, you won't be able to strengthen, they will dwindle and die. they made it this far, so i would say feed until you do know.
what are your temps, day? night? sugar syrup is probably not practical for you, if your temps are too cold, the bees cannot utilize this liquid.
let us know, ask questions, keep us posted!