...Weren't we in the village? I don't think Mari and what's his name would kill genin while still in the Mist Village. Seems like an easy way to get found out.
No, we were in Noodle (I'm 99% certain this was all only to be able to say it was "the Noodle Incident" later on). Shikigami and Mari hatched a plan to make it look like the higher-ups had sent us to die despite there being an actual mission (basically proxy war between Leaf and Mist, Noodle is Vietnam), killed everyone who didn't like Shikigami offing the ranking officer, and then said "good, now everyone who's alive, follow me if you want to live."
Yes there is? If we discuss it with Mari and Kei and they agree, we now know with no danger.
If they agree that only tells us that they agree. And then Shikamaru notices Kei eyeing him suspiciously and things can actually go awry from there with mister superbrains, especially if there was actual foul play. Because he'd be watching for this. Actually, Asuma could have told him to be on the lookout for any indication to that effect, in order to monitor our stability and loyalty, regardless of either of them's implication or lack thereof.
No one is going to accuse any of them. You realize this right? We just want to know privately and internally so we can move accordingly.
If we only ask what Mari and Kei think and Kei doesn't even act any differently at all later, we've kept it private but didn't actually learn anything. The only way that lets us know privately and internally is if Kei and/or Mari already know/s, and then why didn't they tell us already? If we look for anything more substantial than "what do you two think" we're exposing ourselves to serious risks with no counter at the ready.
It's a lot harder to look for stuff later than it is when it's fresh. We're all but guaranteed to never know/find out if we don't at least start the process now.
Akane is a trustworthy source. When we get her back we'll simultaneously have a lot of power of our own, a sudden boost from getting Akane back, and the best possible person to answer our questions.
In the meantime, we can still investigate the lead of the spice-based body odours, if we can provide Canvass with foreigners who'll have different-scenting sweats, or spices directly. I think that was mentioned but didn't reach a resolution yet.