are they getting ready to swarm?..
Could be, but "bearding" is not a definate sign. There is also the possibilty that it is too hot inside for all of them.
Inspection for swarm cells is the best way to tell if they are preparing to swarm. They will slim down the queen so that she can fly and she will stop laying eggs. The absence of eggs and presence of queen cells means they are getting close to swarm.
If it is just a heat issue, give them more space and ventilation. A slatted rack or screened bottom board for the bottom and either a ventilation box or upper entrance on top.