Erwin,
Swarm cells are generally located around the bottom of a frame. They will produce more swarm cells than supercedure cells. Some times they only build a few but most build 5+ cells, most strong hives will build 20 or more.
Supercedure cells are much lower in numbers, generally only one or two. It almost looks like they are trying to hide the cells from the queen. Queens will destroy queen cells if the hive is not getting ready to swarm. I guess they know what the cells are for. Usually they are found away from the brood nest in the upper parts of the hive or on frames close to the outer edges of the hive.
Emergency cells are found in the middle of the frames. And you will find more on the frame that had the youngest brood/eggs on it when the queen was removed or died. They very in number, but most colonies will build 5 or more.
If the hive still has eggs you can remove the cells. If the hive has swarmed or even killed the queen they will still have eggs to produce a new queen with. This is a common practice that beekeepers use to keep their hives from swarming. (aka. cutting cells) Some beekeepers do not like to do this because it is said that it causes undue stress on a hive.
If you do not want to cut cells this is a prime time to split the hive. If they are getting ready to swarm then you can split them and set the new split/hive beside the old one with little trouble of them returning home. Do it in the middle of the day when most of the older workers are out foraging. Take the queen and a one frame of capped brood into the split. Shake 2 more frames of bees into the split. The rest of the frames you want empty so the queen will have plenty of room to lay. You keep the rest of the brood in the old hive since they are losing the queen and it will be 30 days or so before they have a laying queen again.
<What are they up to?>
Kinda hard to tell with the description you gave. If you do have a queen going into the second or third season then it is VERY possible that they are looking to swarm.
If they are trying to supersede her then it will be better for you to requeen them yourself. I have not had but a few hives to supersede a queen. Each time the queen was less then perfect, to the point that I could tell how bad she was.
Do you have Russian bees? They are known to keep queen cells off and on throughout the season. They will build them and even start to raise a queen in them, only to tear them down and start over. The same queen keeps on going and seams not to mind the hive raising cells.
<What should I do about it?>
The best thing you can do to prevent swarming is requeen. Young queen are not as likely to swarm like older queens. Give the queen plenty of room in the brood nest. If she has to search for a place to lay an egg then get ready for them to hit the road. Make sure the hive isnt overcrowding. The bees need room and some where to put the honey. Keep supers on and let them expand. The hive needs to have good air flow too. I have screen bottoms, or you can get a slatted rack to help with the air flow.
<What should I do or shouldn't I have done?>
If you havent done what I said above about trying to control the swarming then you need to start working on that. The bees natural instinct is to swarm. It may take you a couple of seasons to learn the art of swarm prevention. I know I read about it all the time when I first started but it takes some practice. The bad thing about having practiceing is you only have one shot per season to get it right.
BB