Technically, all bands on your account will work on any room you're staying in. That said, it doesn't always work as planned, when it comes to resort-specific tasks. Each resort operates somewhat independently. There are operational options that the each resort can choose to implement or not. One of those is how many Magic Bands a given guest can use at that resort.
The norm is to not restrict the number, but BC/YC tend to restrict it to a single band so that guests cannot hand out their extra bands to friends/family not staying there which would allow them access to Stormalong Bay.
A band will only operate on a single room at a time.
For non-resort uses- tickets, charging, etc. - you won't have any issues, and they are all interchangeable.
Generally, you should be able to use any and all MBs listed as active on your account. Occasionally, there have been issues on checkout/checkin day, but a quick visit to the front desk should fix it.
Note, that if you do experience issues, and go to the desk, you are likely to be told that somehow this is all your fault, as you have too many MBs on your account. This is a WDW myth, but a convenient one for front desk CMs who don't really understand how the technology works. They've been using that excuse since MBs first started.
Again, you shouldn't have any issues, but it's possible, and easily rectified.
Steve
