I had 33-weekers, at 4 lbs., 3 oz. and 4 lbs. 7 oz. They estimated higher in the ultrasounds, so be aware that those estimates aren't always accurate.
Every week counts though, and you're almost at 34!
They were in the NICU for 4 weeks, and had to have artificial surfectant and be on the CPAP for awhile. One had a PDA and had to have a round of medication to close it. It took them quite awhile to learn to suckle.
They were fed my pumped breastmilk in the NICU (I think they added the extra-calorie formula to it), first via tube and then via bottle. Once they were bottling all their feeds and maintaining their temps, they got to come home.
They learned to breastfeed a month after we got home - so for the first month home I was pumping and bottlefeeding. So tiring, but so worth it. Now they're almost one and still nursing like champs!
I know a lot of a lot of other moms who delivered from 32-34 weeks (other monoamniotic twin moms), and I think all of them had at least some NICU stay, ranging from about 2 weeks to about 2 months. So there's quite a range; it just depends on how your individual babies do.
I'm sorry they have to come early, but you have really, really, really good odds of everything being okay at the end at your gestational stage. I hope things go well for you.
Remember when they're in the NICU that they're exactly where they need to be to get strong enough to come home; you are NOT a bad mom because your babies have to start their life in isolettes. You're a mom who is getting them the best care they need.
Don't be afraid to ask the nurses or the neonatologists questions. I found ours very knowledgeable and very able to explain things. I called every night to talk to the girls' night nurse; it was like saying good-night to our girls, and we visited every day (except once, when I had a cold). But we weren't there all day, because of our older two at home. Our twins still bonded with us. If you can't be there every moment, it's okay. Be there when you can, and trust that they'll be okay when you're not.
When you get home, sleep as much as you can. It's good to be physically recovered when they come home from the NICU, because you'll surely need all the energy you can get with two lovely babies demanding your love and attention!