One of the staff is wrong… We assume an awful lot during drill. We assume that all cadets have been taught the same drills correctly. There is no need to spoon-feed.
If being properly correct, you never say how many ranks there will be. That part of the command is “Form squad, quick march” no matter what the number of personnel. As far as drill is concerned, there are always three ranks when forming up.
If you want to move the squad/flight/&c into two ranks there is a movement for that, and it starts with them being in three ranks.
The cadet-ism about forming in 2 ranks if there are less than [insert locally made-up number here] is just that… a cadet-ism.
Whilst, there’s nothing intrinsically wrong with having a local decision where cadets automatically form in two ranks if under a certain number, it’s not strictly by the book.
Contrary to my learned colleague, I wouldn’t personally advocate including extra made-up parts of the command during training. Arguably, during training is when they should learn how it’s going to work in the real world.
One can simple pre-brief them if required… “I want you to form in two ranks this time because there are only 6 of you…” before giving the proper commands.
All that being said… There is also no need to ‘borrow’ commands from a movement (“form squad, quick march” is part of “Sizing a Squad”; it’s not, strictly, a command to be used on its own).
If one wants the group to just fall in, one can simply say “fall in!”; which, if cadets have been trained to know what it means, should have the same effect and is universally applicable.