Is it in the first sentence understood "al cinema"?
I mean, is the first sentence: "Ragazzi, stasera noi..........(andiamo o veniamo) al cinema"?
If yes, the 2 right sentences are:
1) Ragazzi, stasera noi ANDIAMO al cinema.
2) Noi non VENIAMO con voi al cinema, siamo stanchi.
I think it's important for you to understand WHY you have to use "andiamo" in the first sentence and "veniamo" in the second one, so that you won't have any doubts if you are facing a similar situation in the future.
USUALLY, the verb "ANDARE" is used for a movement to a PLACE where NEITHER THE "SPEAKER" NOR THE "LISTENER" IS, while the verb "VENIRE" is used for a movement to a PLACE where THE "SPEAKER" OR THE "LISTENER" IS (OR BOTH ARE).
In the first sentence, a "speaker", WHO IS NOT AT THE CINEMA, is telling a "listener", WHO IS NOT AT THE CINEMA EITHER, that he/she (the speaker) and his/her friends are going to the cinema, so "ANDIAMO" has to be used.
In the second sentence, NEITHER THE SPEAKER NOR THE LISTENER IS AT THE CINEMA EITHER, LIKE IN THE FIRST SENTENCE, so you should expect "ANDIAMO" as well, BUT "VENIAMO" HAS TO BE USED INSTEAD, because the verb "VENIRE" IS ALSO USED TO TALK ABOUT "JOINING A MOVEMENT OF THE SPEAKER'S OR THE LISTENER'S", and NOT ONLY ABOUT "COMING TO THE PLACE WHERE THE SPEAKER OR THE LISTENER IS".
In fact, THE LISTENER IS GOING TO THE CINEMA, and the SPEAKER is talking about "JOINING" (to be exact "NOT JOINING", in this specific case) the LISTENER'S MOVEMENT to the CINEMA ("non veniamo CON VOI al cinema").
And it doesn't matter that they have decided NOT TO JOIN the listener's movement to the cinema (noi NON VENIAMO CON VOI al cinema) what matters is that they are TALKING ABOUT THE "IDEA" OF JOINING THE LISTENER'S MOVEMENT TO THE CINEMA, whether they join it or not. This is enough for them to say "non VENIAMO con voi al cinema".
The same rules explained above apply to the English Language (andare = to go, venire = to come).