I went completely natural at a birth center with my first, but I think, if I were carrying twins, I'd want to labor in a hospital setting just as a safety precaution. Even if baby A is vertex and delivers just fine, you never know what baby B might do at the last minute, and it's good to have a backup plan.
I'd have them place an epidural catheter and not hook it up to the medication pump. But I'd also ask them to do it WAY early in the game, so you're not messing about with holding still for an epidural when you're really in the zone in active labor. And here's the other thing -- if you DID wind up with an emergency c-section, wouldn't you want to be awake for the birth of your baby? If there's no time for the spinal or epidural, they have to put you completely under instead. Not a great option for anybody.
Hopefully everything goes smoothly and you can have an unmedicated, vaginal birth for both twins. I think you'll be able to resist the temptation to use the epidural, knowing it's only there as a safety net for you and your little ones.