You do not give enough info to know for sure, there are several possibilities. But what MIGHT be happening is the first swarm issued 22 - 24 days ago. After that, as queen cells hatched, the bees swarmed themselves out leaving few bees, as sometimes happens, I have seen hives swarm out to where survival of the parent hive is near impossible.
Because the first swarm issued 22 days ago, all worker brood has now hatched. Only drone brood is left because it takes 25 or so days. Mites prefer to breed in drone brood, so the hive is overrun with both drones, and mites.
I would not move bees from this hive to another. There will be little gain for the other hive, but there will be a lot of mites.
It is possible that there is still an unmated virgin in this hive from one of the swarm cells, due to start laying any day. To test, take the advise given & put in a comb of eggs to see if they raise queen cells. In a week, see what's happening & come back to the thread for more advice.
But as a lead up to that, if the hive gets a laying queen or for some other reason is deemed saveable, you will need to do 2 things. One is add some hatching brood. That's because when a hive has a high % drones like this they disrupt the workers & prevent them heating the brood adequately, & the hive dies. You have to add some hatching brood to increase the % of workers to a point they can efficiently run the hive. The other thing is treat the hive with Apivar. There are just too many mites to expect this hive to throw them off & come through OK. Only treat if you go ahead with saving the hive so wait to see if you get a laying queen, but if you do get one, treat immediately, before the mites have a chance to go into capped brood, so they are all exposed to the treatment & you get a good fast kill.
About your Apivar, you say you have "some". Does that mean an opened pack? Once opened, the strips are exposed to air and the active ingredient starts to degrade, eventually rendering the strips useless. So is the pack open & if so how long has it been open?