C'mon,,give 400dabuser a break.. Fair questions deserve fair answers..
I'd use One Shot AF with a single focus point on the subject preferably around the eyes.. Now the problem you have is that you need to shoot two people so it's advisable both are sharp.. You need a smallish aperture of around f/11 to achieve this.. Bring your flash in close but far enough back to get even lighting..
Shoot quite a few frames focusing on different parts of the subject(s) and allow the depth of field to look after itself.. You can also step back a bit and shoot more loosely..This will give you more depth of field at the subject and you can always crop during post processing..
If you need to be asking such simple and basic questions, then you are not even close to ready to be shooting this gig, even if you're not being paid for it.
Why not?? The best way to learn is to be thrown into the deep end..
We don't know who these people are,,could be his friends or siblings..
Sweet Geezus,,how many times did I take s**t photos of friends and family when I was first starting out..