You may also have a problem because they 'Pose'.
This is annoying, because it looks fake, try smiling when your pissed of and you get this evil like smile

.
Try any of these.
Take the pic just when they are about to smile, apparently it gives you a nice relaxed smile.
Take a second pic right after.
I mean take another pic in like the next second, everyone should be natural then.
Dont let them kno when your taking the pic.
Try to make them think when your taking it and then take it later...e.g. 1, 2, 3, then take the picture on 4 or 5

.
Take the pic on from your waist.
This will catch people of guard, as long as you have the camera aimd properly should be ok
