Bees on the front could be several things. If they get too hot then they will gather or "beard" on the front of the hive, not really something to worry about.
Couple of things to do. Give them more room. If you haven't already, throw on a super to give them more room to expand. Second, they won't swarm without a new queen (usually) so check and see if you have any swarm cells. If you do then you know that they are preparing for it. There are several things you can do at that point, but before discussing that (and there are other threads that have talked bout this before or Michael Bush's web site on this topic) do the basics first. Once again, give them more room and check for swarm cells. Good luck.
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