Discussion Before Death

How might a discussion go before one person kills another? Or what might it look like? I have a group of characters all sitting together at a night club and two of them are brothers planning to kill the other five. They have to act chill beforehand so no one gets suspicious, but I also want the reader to feel like something's up with their behavior. I'm not entirely sure where to go with the preceding discussion, how to make it seem natural while still giving off a notable amount of oddness. Any suggestions?

 

So tell me a little about these killers. What kind of killers are these? Do they have a motive? Are they more like thrill killers? Are they serial killers? Because depending on what they are, will ultimately decide on how they'll act.

I would suggest a good place to start is by watching Road to Perdition. You can probably guess whose character is there to kill who.



First thing I want you to note is how takes its time to build the scene. Note how the killer talks about something most people are uncomfortable talking about. But he's talking about it so casually.

See how the killer is hyper focused on his victim. You know he's not there to order the special. Ordering food is a distraction.

 

The killers are new to it, with a reasonable motive. One is nineteen, the other is twenty-one. They're brothers. And I do like the idea of having them talk about something uncomfortable but casually speaking about it.

 

I admit it: I've never personally murdered someone.
You can consider the psychological process the killers are going through and base their discussion on that.
If you are hyperconscious of doing something wrong, you automatically feel like everyone's seeing right through you. That's why you (subconsciously) try to compensate by seeming more casual, like talking about meaningless things.
At the same time, feeling like you're being suspected makes you nervous and you can't keep a clear head, so probably you might answer less smoothly to questions, or talk about things in the immediate environment because you're too stressed to think of anything else.
Just my 2 cents