Villagers will not path-find to empty beds to sleep.  My village is quite large with over 75 villagers in total (at last count) and there are plenty of empty beds, but the villagers don't walk to the beds or sleep on them even though they have allocated the bed (green stars appear).  Sometimes the villagers allocate a nearby bed that is the other side of a wall, but will not walk the short distance to it if the access door is further away than the bed - they almost always walk in the wrong direction and deallocate the bed again.  Other villagers will not allocate an empty bed even if it is next to them!