Lots of things smell bad. Some of those are green.
Unless you absolutely know this is pot, then that's what you've got - two adults talking about something green that smells bad.
But let's say you know, for certain, yadda yadda. Well, what do you honestly think the consequences will be, if you start talking? Do you feel you have a decent home life? Love your parents? Aren't hit by them or otherwise abused? Going to be able to go to college if you want to? You've got shoes on your feet, a roof over your head, food on your plate?
Then screaming about this to the next 15 people you meet means that there's a possibility that CPS will be called.
I am not saying that you should turn a blind eye to wrongs. And I am not saying that you should be a party to things, particularly if they make you uncomfortable. But think this stuff through - and talk to your parents. You know, the people who will be most affected by this?