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Blueberries are naturally hardy, but the roots may still require some protection during winter by wrapping the container in blankets, bubble wrap, or quilt batting. Alternatively, you could sink the container in the ground over winter by digging a large enough hole to accommodate the container (up to its rim or a couple inches). As long as the roots are protected, they should live through the winter just fine.

If you decide to plant them in the ground, their care may be variable, depending on the type you have. Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm

They should not be pruned back to the ground. This article has information on how to prune blueberries and when to do it as well: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm

If they were planted this past season, you can mulch the base of the plants to help keep the new plants winterized. But, if they are established (more than 1 year old), you do not need to do anything for them.

The first thing to do if you're having problems with blueberries is to get a soil test, to make sure they have the pH and nutrient conditions they need. This article has basic information: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-fertilizer.htm
Then check the area where the affected bushes are (or were;) is the area low, or shaded, or is something affecting the drainage in those spots? Then look at leaves and roots for signs of disease or insects. Here's an article on diagnosing blueberry problems: https://extension.psu.edu/plants/gardening/fphg/blueberries/diseases
The county extension service might be able to help you identify problems, probably if another bush starts to fail. This link will help you find the nearest office:
https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm

Blueberries like low soil pH; otherwise, the roots become blocked and the plant cannot take in any moisture or nutrients and will quietly wither and die. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blueberries/growing-blueberry.htm

https://www.gardeningknowhow.com/edible/fruits/blueberries/lower-soil-ph-blueberries.htm

You can cut back the plant, but I would not do so all at once. Every year, cut back no more than 1/3 of the oldest canes, until you have got the plant back to a manageable size. Here is more information on pruning blueberries: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm

As for the lack of fruiting, this could be attributed to your soil and fertilization. Too much nitrogen will result in little to no blooms or fruit but plenty of growth. Increase the phosphorus content in your fertilizer, or add some bone meal to the soil to help encourage additional flowering and subsequent fruiting.