i was in that exact same boat. like, i could have written your post. it was bad...
one night, i just got totally fed up. it was obvious that the nursing back to sleep wasn't doing the trick any more. until then, i was afraid to NOT do it, because it was all that i really knew. anyway, i got to my breaking point and decided to night wean. it was 2-3 long nights of getting everyone adjusted, and then, magically, i kid you not..... they were both sleeping through the night. honestly and truly.
a disclaimer: my boys were down to nursing only to sleep and at night at that point, so this weaned them completely. i don't know if that has anything to do with it.
but yeah... since then, they've been sleeping through the night consistently. it was an adjustment at first, but it was just what we all needed. that, coupled with moving them on to mattresses on the floor in their room, so that when they do wake, i can just pop in, lay with whoever is up, and slip out when he's sleeping (if i don't just pass out there myself).
i am not advocating weaning or anything, totally a personal choice, but that is what did the trick for me. my boys are now 20mos, sleeping by 8 (i lay down with them, pat them, sing, whatever, usually takes about 20min), and they wake up happy around 6:30 or 7.