On the second sig there's a general low visibility, which you can make up for with maybe a fog affect that covers the legs of the zombies in the back, maybe darken their bodies in general, just to show some distance, also add a little fog to the front man just to keep some consistency, not too much though since he's the main attraction. Looking at it again, the characters in the background are lighter than the one in the front, makes it look a bit odd. You could also lighten up on the snow just a bit within the body of the picture, maybe make some of the bigger ones blurry while the smaller ones could be sharper, just to create a bit of focal point effect.
On the second one you could go for some smoke and laser lights that go over the main characters a little bit, make it seem like their in that background instead of just standing in front of a picture. Also, the guy on the right is significantly taller than the girl, but their features are very close in size, maybe find another pic that doesn't draw the attention of the pic so much, the second pic looks like the secondary characters are far away, if you could recreate the first pic to have the same effect it may look just a little bit nicer. Maybe go for bringing the woman up and forward, so that she's standing in front of the man in black. If she's supposed to be an escort try getting them to stand back to back and closer to each other, if they looked like they were walking, it would look more natural to have them facing the same direction. If you're choosing the girl for a specific reason than work with the pic you have, however I would find someone with a matching facial expression, chick looks inviting and the dude looks like there's trouble afoot, since they're both looking the same direction they should probably have a similar expression.
That's what I'd do, and don't feel obligated to do all or any of what I said; I ramble to give you ideas, not because I'm desperate for you to take my advice.