One of my hives made it through the winter, but has a small population. There are two frames with brood on both sides, and enough bees to keep the brood well covered. They are raising some drone brood now. The hive had a high mite load in the fall but got treated with strips and has shown no mites on the sticky board since. They have eight frames of honey left from winter, and are hauling in nectar and pollen as best as their numbers allow.
What can I do to help them build up at this point?
If the honey frames are close to the brood, let them grow.
Perhaps consider confining the bees into a smaller space, reduce the entrance as much as possible to cut back on any drafts. If they're in a double deep, put them in one level unless you're breaking up the cluster. Perhaps use a follower board or put them into a nuc if possible.
Off topic, but it looks like the Bix has blasted off!
I like the new avatar :)
Obviously if you have a spare a frame(s) of brood from a strong hive to give to the weak hive, it really helps to get them going; along with what the others have said. The more numbers of bees you have in a box, the faster they build up. One deep frame has over 6000 cells. Not all are filled with baby bees, but still adding a deep frame of brood to a weak hive greatly boosts their numbers (as the brood hatches out).
As Michael Palmer was preaching in his nuc presentation, if you have some spare nucs in the spring, you can use frames from them as "bee bombs" (his name) to boost weak production colonies in the spring.
I like this idea. Next inspection this will be the plan.