What I mean is if your aim were to increase your hives rather than produce honey but to do it in such a way that did not risk your colonies then how many is likely or feasible in one year to produce? And using what methods?
Every year is different, so I don't think you'll have much success if you have only two colonies to begin with. But my suggestion is that you sacrifice one of your colonies as an experiment. I'm no expert, and my bee math is poor, but why not:
Select your strongest colony, and take out the queen plus three frames (with bees) and put them in a 6-frame hive (plus foundation). Then wait 10 days for the now queenless colony to make capped queen cells. Then split the queenless colony into smaller colonies (all of them in 6-frame hives), and make sure there is a queen cell in each of those colonies. Why don't you make two 3-frame colonies and two 4-frame colonies (putting foundation in the empty slots), to see the difference? Then wait 20 days and then check whether there are now laying queens in those hives, and if so, overwinter them.
Or, if you're concerned that may you not get enough queen cells, after you've removed the queen from the main colony, immediately split the now queenless colony into 4 hives (6-frame boxes), and wait 10 days for them to create closed queen cells. Then split up the frames and bees and queen cells into the multiple 6-frame hives, and wait 20 days before checking if the new queens are laying.
I think you barely still have time to do this (if you start by 1 August, then the first new bees should be hatching by 1 October. You can of course boost your nucs a bit by adding frames of closed brood to them from your remaining strong colony.
I remember reading somewhere how many frames are needed in a nuc to be certain that the nuc will survive the winter, according to the month in which the nuc is made. I can't recall exactly, but it was something like June = 2 frames, July = 3 frames, August = 4 frames (i.e. if you make the nuc in August, you need to start it off with at least 4 frames). Can anyone confirm this, please?