You might be surprised at how your skin bounces back. I was lucky that I did not get stretch marks with either of my pregnancies. I will admit that even though research claims it doesn't help, I rubbed lotion on my belly everyday.
Now, as for some issues with extra skin from stretching. I do have that. It started with my DS though, and he was a singleton pregnancy. It was mild with him and it seemed to be slowing going away when I found out about the twins (he was 5 at the time). Now, I have the saggy baggy elephant if I bend over. Sitting is such a pain because I look nice and thin standing up, and then I have rolls when I sit. All because of the saggy baggy elephant! I also have a nice muffin top now no matter what size pants I wear. So anyone that says muffin top only occurs when your pants are too tight has never been pregnant EVER!!! It drives me nuts because I cannot wear my pants 3 sizes too big to stop the muffins from appearing. Blah!
Yes, your body will change. Yes, sometimes pregnancy does things we absolutely hate to our bodies. However, the kids tend to make you forget about it (at least until you put on the pants and see the stupid muffin top!!!).
I had triplets and it's not that bad. I have some overhang which sucks, and I'm using Mederma to help the stretch marks, but it can be done w/o getting real bad twin skin. My stretch marks didn't show up until the late 20, early 30 week mark maybe. It was pretty late and let me tell you I was BUMMED! My pre-pg pants fit, they just fit different. Of course, I need to start doing some sit ups too, but regardless. lol I also wanted to say it took quite a while for my pigment to work itself out. It hasn't totally yet, but that was the worst part for me. My navel ring hole was nasty nasty bruised brown looking, just pigment. Ick. But that too has gotten much better.
Good luck! I hope your skin is nice to you.