Side Bb is the standard fingering, and also the chromatic. Use it in scalar passages and when not followed or preceded by a RH fingered note.
Bis is for non scalar passages, and when not mixed with B nat.'s. Honestly I probably use bis a little more than I use side, and there was a time I used bis a lot more.
1/1 is only for special circumstances as it is out of tune and tone. I only use it for very rapid Bb maj arpeggios when I can just anchor the first finger of each hand. This fingering used to be really pushed as a standard fingering by some older players and teachers (older when I was young, which now means REALLY old), and I can only think that it came from either that most sax players started as or also played clarinet, or that there was a brand/model of horn that this sounded good on. On my Mark VI it does not.
1/2 is like 1/1. It does not sound good, but is handy when playing fast F# arpeggios. You can anchor the RH 2nd finger and go to town.
Back to your original question. Don't teach 1/1 (or 1/2) until the need arises. I would go ahead and introduce bis fairly early - first time you deal with Bb and RH fingers in succession. It doesn't matter when you introduce it (if they haven't discovered it already - I think I found it on my own wondering why that little pad was there), most players are going to jump on it and use it a bunch/too much regardless.