Since I bought 2 of them in the last spring and the other 4 are splits of from those 2, I have no clue about their genetics and wintering abilities. However, I'm relying on the fact that the guy from who I bought my two hives is raising his own queens and his apiary is very close to mine. So I expect some locally adapted genes

To be honest, I was expecting to find one dead colony, which was only the honey producer of last season and had a very low population. Its population dropped significantly after honey harvest in August and couldn't produce enough young brood for winter, which was typical mite effect expected in autumn. But it seems it has tolerated the varroa load so far. I still think it won't make it but if this colony survives, I will take good care of its queen.
BTW, there were a lot of bumblebees around checking entrances of my hives; some even were going in and out of hives. I guess they were either trying to steal food or looking for their new nest for the upcoming spring.
I took a photo of one of them.