You can certainly teach one sax, even if you play a different one. In fact, an awful lot of sax players will possess and play at least a couple in the same band. Alto and Tenor are the most common.
The main problem is that Alto and Baritone are both E♭ instruments, while Soprano and Tenor are B♭. This is compensated for by use of transposed keys in the written music. And means that anything you play from the dots (on Tenor) will not sound in the same key as the student playing on Alto. So demonstrating will be a challenge. What the best players do is transpose at sight, in order to play the same notes as someone playing the 'opposite' instrument. Might be a golden opportunity to add to your armoury another sax - the Alto! The money from several lessons should pay for it. And it's probably going to come in useful for gigs, too !
In fact, a lot of the sax players I play with also 'double' on flute and clarinet, as the fingering is similar, - but not identical - and obviously the embouchures are different. But, more strings to their bows, so to speak, and teaching, well, why not? They're more than half way there.