First, congratulations on the birth of your babies! A vaginal birth with twins is something to be very, very proud of, and you gave your twins such a good start during an otherwise difficult time.
Your feelings are so valid... our preemie was our only child, so there were no other children to worry about, and I can't imagine how difficult this must be for you. Is there anyone who can come over and help you with your other children? Are they having a hard time understanding what is happening? I don't know how old your children are, but sometimes it's helpful to let them be constructive - perhaps they can spend some time each day drawing pictures or writing letters for the babies.
It is so hard to look around the NICU and try to absorb everything that is going on. Have you asked your doctor when your babies will be able to share a bed? Different NICUS have different requirements when it comes to this. Pumping sucks, and there's just no way around it. But at the same time, pumping is one of the absolute best things you can do for them right now, and it is something that only YOU can give them. Machines, doctors, and nurses can't begin to match what you are doing.
Someone else mentioned that a lot of NICU mamas crash when they get home. This is so very true. I second the suggestion that you try to find a local support group or get friendly with the other NICU parents. When your babies do come home, be ready for a flood of emotion and try to have help lined up- either extra family and friends around for support, or a few appointments with a therapist. Just monitor your feelings and act accordingly. Some people feel better keeping a journal or blogging. I found that my journal really helped me deal with the daily emotions.
And I know how hard it is to see other people taking care of YOUR babies. Please try to remember that these children are in fact your babies, and that you will be a big part of their daily care very soon. No matter what, they absolutely know who their mama is. It's so hard to feel so completely out of control, but try to identify the things you DO have control over, and jump on it! Are the babies wearing clothes yet? Are they on an open bed or an isolette? You can add your own blanket to the top of the isolette, and if they are wearing clothes, many NICUs see no problem with letting the babies wear clothes you bring in. Are you able to help with cares yet? Sometimes being able to do something as simple as changing a diaper makes a world of difference. Eventually you'll be able to breastfeed and kangaroo, and that will probably be one of the best days yet. You can also read books aloud, sing, hum, etc. All of those things will soothe your babies, and your voice is something that is so familiar to them (and again, it's something that the hospital staff can't provide).
Please keep us posted, and good luck to you.
"In the depth of winter, I finally learned that within me there lay an invincible summer"