Hi OP,
I'm also a twin mum, my boys are now one.
Although they were not prem, here are some ideas that may help you that sort of worked with our boys...
Raise the cot on one side so she is tilted, it may be reflux and settle down. DT2 still needs his slanted some nights.
Try putting her to sleep on her side, this is the only thing which would work early on, we turned him onto his back when we were sure he was asleep.
Shifts between yourselves... I went to bed when DP got home at 6. He stayed awake until 1am so I got 6hours sleep, then he went to bed until he had to get up for work. I slept when I could in between these times.
Split them up. You'd be surprised how much they might be disturbing each other. (Also can tilt one cot)
If one baby wakes, wake the other. Try and get them in-sync.
If one baby wants a feed, feed the other. That way (hopefully) they both should want feeding at relatively the same time next feed is due, gives you some down time.
Get a decent twin feeding pillow and feed them both at the same time.
DO NOT feel guilty about leaving one (or both) to cry. It won't be forever and this is something you just have to live with sometimes to survive the first months.
All twin mums will tell you, it does get easier. One year in and they now do their bottles by themselves. Sleep through the night and give me a two hour break in the afternoon.
You ARE amazing.
Feel free to PM me any time if you need to chat. Alternatively check out the TAMBA website, they have a load of info on there specifically for twins and a freephone support phone number, manned by twin mums.