D.C.
Wow! Congrats on the new little ones.
I would suggest consulting a Lactation Consultant. I'm pretty sure I can get a reference for you from my local consultant.
You are wise to be wary by the feeling engorged. It is a problem. You don't want to develop mastitis or plugged ducts.
Right now, your body knows its feeding two babies but a pump just doesn't respond like nursing. If you can get yourself into the NICU to visit and nurse the babies, that would be wonderful. Pumping and hand expression can help relieve the feeling engorged. Why not take pumping off of a schedule and do the pumping every chance you get? Maybe a compromise would be to pump every three hours _and_ pump, but throw away, a small amount at those "30 minutes later" times when you feel engorged.
Wishing you the best!