Wow, that must be really difficult!
Some suggestions (that you've probably already thought of):
Do you drink anything caffeinated? Especially when fighting exhaustion, it becomes tempting to do so; but it gets into the milk and can keep baby awake.
Have lavender in the room. Its scent is relaxing and may help.
Also, is the diaper wet each time the littlest wakes up? Might be hyper aware of that. Ours was. I got flannel inserts for extra absorbancy at night from www.greenmountaindiaper.com
and that seemed to help.
What about teething? Ours became really restless about that time, even though he wasn't apparently in a whole lot of pain. He just didn't sleep well.
He also went through a stage of only napping with my boob in his mouth, then waking. It ended eventually.
When I was having a little trouble with milk production, I was taking a tincure of hops (it is a galactagogue! and soothing). It is really bitter, but it made sure I had plenty of milk and it is also calming and soothed my pixie through my milk. (http://www.herb-pharm.com/
for information and www.flowerpower.net
, my favorite herb source)
Foot massage? With a little bit of fennel essential oil added to the Weleda Baby Oil (which has chamomile and calendula and smells great). Ours seems to love having his feet played with...most babies do, I think.
last but not least...is there any way you can get someone to do a "napping co-op" with you and come over and play with your energizer bunny for a couple of hours at your house while you nap? And maybe you could return the favor in kind or some other way (like a pot pie
or a cake or something)?