I initially tried the technique of covering up one photo and seeing how I felt about it. On their own, I feel like I'm looking at an outtake. As a dyptich, I really like what is happening. There is an awkwardness and discomfort in Natasha that stays consistent in the two frames. These aren't out takes of some pretty girl who forgot to strike a pose for a frame, this is how Natasha really is. She gazes out, lips pursed, almost smiling, maybe attempting to see if that special someone finally noticed them. Or is she simply in that stage of innonence and confidence--Natasha's pose and gaze in the left frame suggest self-assurance, maybe asking "whattt are you loooooking at? (insert girly voice)" but at the same time the resting of her lips and showing of braces contradicts her confident attitude. But wait, is it only the face that tells the story? No way! Look at her sunglasses. They're oversized, white, and dark. Natasha accessorizes it with a red ribbon, clearly matched with her oversized red necklace and red bag. She sports the classic red and blue look with the trendy fitted t-shirt from Urban Outfitters: a penguin with a, wait for it, red heart. Our friend Natasha obviously cares about what others think about her. Confident? Maybe. From this dyptich, it seems to me she is that girl who is self-conscious, insecure, and cares what her friends think about her, even if she denies it.
It's also important to respond to the fact that this is the first dyptich I'm seeing in this project. How will this correlate to the other characters you're building? Why is it Natasha that gets a dyptich? Does Kate get a dyptich, too? I like what you're doing in this portrait but I'd consider how much it stands out.
I still don't understand why you need an 18mm lens. I feel like the normal 50mm should cover you. 18mm is rather wide. It will create more physical distance in your images. Does Ryan McGinley walk far away when shooting? Does Nan Goldin? Not in the work I've seen at least. Part of their success is dictated by how close they're are getting. I think you're gaining intimacy with your subjects. And even though they don't know how wide your lens it, the images themselves might appear too distanced.
The double exposures are a must. You produced some amazing images with Kate. Let's see more of that. And yes, go for the strobe light. The on-camera flash isn't powerful enough and can't be manipulated like a strobe can.
I like the 35mm format. I don't see any reason to switch to the Hasselblad while shooting on location. The spotaneity and movement that the 35mm allows you to do works in your favor--you, as the photographer, can move around as much as you please and don't have to ask your subjects to "hold still" while you fiddle with the Hasselblad. The 35mm allows you to just watch the moments and snap away.