(Assuming you meant N1 instead of N2.) Yes, I'm sure they can. Both N1 and O2 are forward hexes for those units, neither is marked with a Range counter, and I can't find any requirement that units stacked remain stacked. A25.232 talks about "each unit" having to do one thing, not "each stack". Further, in the second Impulse of the example it says "at least one of the units in" not "at least one of the stacks in", and the two 237s in O2 split into N2 and O3.