Backstory, fiancé is a 5+year beekeeper, I’m in on my second year. We left winter with 6 hives. We share 1 beesuit, and the other makes due with a mosquito net and rose pruning gloves. 

2 weeks ago we arrived to our apiary as we had been informed a swarm had settled behind one of our smaller building on the summerhouse. A couple of hours of preeping and scooping we got them to settle into there new home. 
We assumed it was our own swarm so we immediately checked on our 6 other hives and found bunch(10+) of swarm cells in 4 of them even though we added an extra full deep box for honey just 7 days prior. 
Well… it’s a natural drive for them. Verified that we had queens, culled the queen cells, and made an emergency split on our largest hive(leaving 2 queen cells). Didn’t find any hatched peanuts or population loss so a bit confused if it actually  was our swarm but nevermind- it’s ours now. 

6 days later we are back. Neighbor informs us and shows pictures of a huge swarm from the 1 days prior hanging out in there oak tree. That ship had obviously sailed.
Open up the caught swarm from last week and it gets super evident it wasn’t ours, queen marked red, we mark all ours yellow- great!!! Bonus bees.
Back to our ordinary hives. Open up 1/2 of the split- looks great, lots of eggs and other larvae.
Here maybe comes the mistake. Opened up the queenless half of the hive and they were super super angry. Pulled a fram, saw a covered queen cell, closed it up. Didn’t inspect all frames as they were out for murder. It’s late, so we decide to inspect the other 5 hives in the morning 
It’s 8am, I’m mucking around in the hive next to the queenless one doing my ordinary check and cleanup of queencells. Saw something that I didn’t like, went to get my partner. In the 3 minutes it took to get him, the queenless??already split hive had initiated a swarm. Quickly swapped clothes so that he had the be-suit and I scurried of to follow them to wherever they went. 
Partner closed up the hive I was inspecting and braves the queenless, split and now swarmed hive. Finds one hatched queencell and still one unhatched cell, several queencups(but younger) concurrent with emergency cells after split , no larve, no eggs. 
Why did our split hive without a queen swarm straight away when the queen hatched? I’m assuming she is still virgin? How do we treat the swarm now that it is caught?
Sorry for the long text 


 

Swarm of a already split hive?