You usually want to make sure you're not harming your allies when you do stuff. Usually.
But sometimes you don't know that what you're doing will harm them. Or at least, your character doesn't know, even though you the player know.
So for proper player/character separation and avoidance of metagaming, sometimes you just have to do something that you know could have bad consequences for someone in your party.
Try not to snicker too much when doing so. A little bit is okay.
Commentary by memnarch (who has not seen the movie)
Finn wants Chewbacca to escape? I'm all for that as I like Chewie, but it doesn't feel like it lines up with what he said before. Maybe Finn is meant to be having a hard time being a traitor here?
There we go! It would have been a disappointment if we didn't have anything explode after the plan of setting up explosives. I'm not sure what exactly this will do to damage a base the size of a large moon, but I'm sure it'll do something useful. Maybe it'll be something that interacts with the part Rey took earlier like further its ability to move around or aim the weapon. I don't think we'll get to see the base explode though; this feels way too late in the movie to get an ending with that happening now.
Pete's just whining too. This hardly seems like kill stealing. Rey doesn't have any abilities that'd call out specific enemies and Pete didn't claim those troopers as his. If he wants to make it a competition, he really shouldn't complain if he starts getting beaten.
Rey: I open fire too!
[SFX]: Pow! Pow!
Finn: Good idea! We provide cover for Chewbacca so he can escape.
[SFX]: Pow! Pow! Pow!
Rey: Oh. I was just racking up my kill count.
Chewbacca: I head out this exit. Do I know they’re up there?
GM: Hmmm. You would have turned before they started firing. So, no.
Chewbacca: I hit the detonator.
GM: The platform Finn and Rey are on shudders violently.
Rey: Hey! We were providing you cover!
GM: A blast flings a trooper over a railing and into the pit.
Rey: And you’re stealing my kills!