I'm not disagreeing with the replies above, but I think it's sometimes quite difficult for new beekeepers to be comfortable with not knowing everything is as it should be. The main problem is, at this time of year, there's less chance that interfering is actually going to be beneficial, and if you can't react to what you see, there's no point lifting frames other than to remove the apivar. As you said, being sure a hive is suitable for uniting is difficult when it's cold for inspections, eggs aren't readily available as test frames, and there could be multiple queens per hive due to late supercedures.
It sounds like you should get through winter with at least some of your hives so, that should give you some confidence that you can let the others sort themselves out, or not as the case may be. In previous years I have done the wrong thing when I thought no eggs in autumn required action. It turned out there was a queen present who was on a break when I thought she would have been making the all-important winter bees.
I hope it works out whether you decide to take a look or not.