Post Swarm Advice

We have three hives, two are new nucs we purchased a few weeks ago from a breeder in NW Arkansas. The other hive we obtained last year as a nuc off a strong feral hive that the local beekeeper's association removed from local Channel 5 News building. They survived winter strong and have taken off this year. We added a honey super three weeks ago and they have already built out all the comb and started filling it. However, I had not had a chance to check them for about two weeks because I have two girls graduating high school this Saturday, and in the last month the two girls had gone to four proms. Plus I homeschool my 14 yo son (who is my chief beekeeping helper). But, suffice it to say, its been a busy few weeks.

They built up quickly this spring. We had added a super three weeks ago and it is all built out and they are beginning to store in it. But in checking yesterday, noticed they had back-flled some of the brood hive with nectar and pollen instead of brood. I realize now that this was a big sign of impending trouble.

This past Saturday we were working in the back yard and all of a sudden there were hundreds and hundreds of bees flying around us. Well, apparently we had a swarm on the super strong hive. Unfortunately, I had missed the signs and the swarming group landed in an oak tree about 40 feet up.

So here are my questions:

1. Bees were very aggressive. Why? Had planned to open hives Saturday to check them anyway. When we did, the bees from this hive were very aggressive. Stung multiple times (first stings since we started keeping bees last year). Couldn't smoke enough. This hive has always been very docile, easy to work with.

2. Should we go ahead and split the hive or take a frame or two of brood and switch it to one of my newer, weaker hives, replacing frame with foundation from newer hive?

3. What should we do now?

Sorry this is pretty involved for our first post but would really like y'all's advice.

Thanks, Helen