You don't say where you live so I can't say about winterizing them. There are many ways to keep potted roses through the winter though.

Both over watering and under watering can cause the leaves to yellow. So does lack of enough sun. Any of those things could be the culprit. Make sure that pot has very good drainage. Roses like water but do not like to have their roots sitting in a pool of it. Let the soil get fairly dry on the top between waterings.

I'm not sure what the brown spots are but check the undersides for very small dots. It doesn't look like you have spider mites because I don't see any fine, dense webbing but you never know.

Overall the plant looks pretty healthy. You have a lot of good new growth there so I wouldn't worry too much.

Do you have a garage? If so put them on a shelf inside the garage (not in the window) for the winter once they go dormant. Give them some water about once a month all through the winter. In the spring when they start to show signs of growth again take them out into the daylight. If you don't have a garage then probably the best thing to do would be to dig deep holes and completely bury them, pots and all, in the ground for the winter and then dig them up next spring. You can lay them on their sides to bury them but you need to make sure there is a good 6 to 8 inches of soil over them. And a thick layer of mulch over that wouldn't hurt either.

As far as planting them permanently in the ground it depends a lot on how hardy they are. The bad thing is that those grocery store minis aren't really bred or tested for hardiness. Some of them can do just fine but there's no way of knowing until you try. The good thing about them is that they are on their own roots so that even if they die back completely to the ground any thing that comes up from the roots will still be the rose you bought. As a general rule minis are fairly hardy, but like I said, zone 3 is tough.

Good luck and keep us posted on how they're doing!

Spider mites can be controlled by washing the plant down with a hard spray on the underside of the leaves. It may help to spray the plant with soap solution (total coverage) and follow up with the sink sprayer. Wash the plant once a week and spritz with plain water frequently. Keep in a cool location because the humidity will be higher there. They must have a half day's bright sunlight. Keep them outdoors in summer but protect against temps below -2 C, which will burn the soft growth.