OK, here is the way that I like for making up fly-back splits. I thought I'd post it to share as I get asked about it now and then. These can be done when you have a hive of 2 boxes in strength, and works better when a flow is on, but can be done with feeders if needed.
Doing a flyback split
OK, here ya go...
Take with you a box with 10 frames of foundation, 2 top boards and 2 bottom boards. Remove the 4 center frames of foundation, setting them aside for now. Go through your 2 box hive, and get a frame that is full of open nectar and put in the edge of the central space you now have in the hew box.
Next, find a frame of drawn but mostly empty comb to put next to the nectar frame, this is so the queen will have open cells to continue laying. This is important, you don't want her to slow down or suddenly have to stop laying.
Next to that open cells frame, put the frame you find the queen on, with her on it.
Next to that, put in a frame of sealed/emerging brood. This gives the queen young nurse bees to help with the brood she has and will continue to make.
Set this box on it's own bottom board with new top board or boards, in the spot that the 2 box hive was in.
Now, grab the 4 frames of foundation you set aside, and the spare top and bottom boards, and bring them as you move the rest of the two boxes remaining to new stands. Equalize those to box's frames with each other so they both have frames of: eggs/youngest larva, older open larva, sealed brood, and stores. Put a frame of foundation on each outside edge of both boxes, that takes care of the four frames of foundation you had extra from making up the queen's artificial swarm box. Set them on their own bottom boards and give them their top boards.
The queen you left in place will get all the foraging aged bees from the two boxes you moved away. She'll get the most of them the first day or three, but will continue to get some for two weeks, since bees go back into the hive for two weeks after their first orientation flights before they become forager aged. The old queens bees will draw comb, they have to in order to keep the queen laying. This has created an artificial swarm with a head start of a bare 4 frame nucleus in the center of the box.
The two boxes you moved to new stands will make their own queens. They will lose their older foraging force to the old queen's swarm box you made. This leaves younger bees in them which are the best for making new queens, and for feeding all the open brood they have. These two also got most of the stores frames, so they will be fine with stores to keep feeding open larva and making new queens.
In 12 +/- 1 days new queens will be emerging in the two new hives. Check them on day 9-11 after making them up to be sure they both do have sealed queen cells. The queen will emerge and be laying 2 weeks after emerging, sometimes up to 3 weeks after emerging, but usually after 2 weeks. So, that will mean you should have eggs in them from new laying queens 28 days after setting all of this up.
You should end up with the original queen hive, and 2 additional hives with 2 new laying queens, all 3 full in single boxes. Depending on the time of year in your area, you may need to start feeding. Check the original queen's box 3 days to a week after setting this all up, if they are not drawing comb yet, then they might need a feeder at this time to draw comb. The other two hives should not really need a feeder until you see eggs laid from the new queen. This way, the danger of robbing is greatly reduced by not having a feeder on a non laying queen hive. Once they are laying, feeders can be given if needed. (I am assuming there was a few frames of stores in these boxes when they were made up.)
If you can follow all of this, then it may be an option for you to try. If you feel it's a bit much at this time in your experience, then it's something you can think about for next year. Good luck with your adventures in beekeeping!