The punctuation depends on whether you're writing for an American or British audience/publication/publisher; so you'd need to establish this first. If this isn't specified or it's global, it's your choice; however, it's only correct as long as you're consistent. So your line would read either:
(UK) When everyone uses 'I's' but never 'we's' OR
(US) When everyone uses "I's" but never "we's".
Apostrophes are always single, of course, and keeping them lends to the clarity of your line.
Also, opposite quotation marks are used for quotes within quotes. So:
(UK) 'She cried, "Hello" as she came into the room' and
(US) "She cried, 'Hello' as she came into the room".
I thought I'd mention this, just in case it's confusing if you encounter it in the future.
Of course, in poetry, punctuation is sometimes viewed as optional and there are poets who use this to their advantage too. Hope this helps anyway!