Hello,
here are good arguments why you shouldn't talk about your hands or exchange any information about the game privately, almost in all game.
First of all, the playroom has been foundamentally built upon the principle to make digital adaptations of card, board and dice games that you can play at a real table, with real people physically present at the same place. No more, no less.
Of course there are exceptions, ducks' race is probably physically impossible, and we have arcade mode reserved for audiogames.
However, I have always been and am still quite attached to keep this in mind when possible (except arcade mode of course). Exploding kittens isn't an exception, it's a real existing game, you can order a physical deck, and given that you put braille or whatever on the cards, you could play it.
Given that, obviously you can't talk or exchange information privately to yourr teammates without notice, and if your opponents notice any sign of communication under the table, it's obviously cheating.
Why not allow private talk. But in this case, you change the spirit, you change the game completely.
But wait, there is more. Let's say that we allow private talk. Exploding kittens is designed to be fast-passed, i.e. you shouldn't take ages playing your turn.
Obviously, while you are writing to your teammates, you don't play, breaking the whole dynamic of the game. And even if you are on voice chat, it's kind of over-exagerated thinking time.
It might be acceptable in a game where you can (and should) take your time playing your turn, chess for example. But probably not in a game where you are supposed to play quite fast like here.
So, now, after this post, I'm pretty convinced that Exploding kittens can't be reasonably played in teams, except if we create or use other cards with teamplay in mind and/or change the effect of existing cards.
A variant of divination where the whole team could see the cards could be one of them. Maybe such an extra pack exists, but if not, we can't just throw a few modifications like that and hope that it will work well. We have to think about it, it can't be completely random trial/errors.