Greg V is right about just needing one subscription, and I'll also add that the Roku player is very small, and therefore portable if you have easy access to an outlet. You can leave an extra set of cables in each TV if you can't reach them easily.
Also pay attention to the bandwidth needs. If you are streaming HD, I think you need at least 4MB. And be aware that some internet providers only advertise "up to" a bandwidth amount. Cable in particular can slow down quite a bit if your neighbors are streaming as well. Mine drops off noticeably in the evening, though I have a backwoods local cable company. If you don't have enough it'll drop back to SD and even lower quality SD if needed, and it may stop and buffer up once in awhile.