Wow - I am right there with you. DD2 just turned two. Starts the night in her own bed, moves to ours between 11pm and 1am. Won't let DH put her down or get her or soothe her at night. And DD1 is 5 and is a terrible sleeper so her sister's middle-of-the-night conflicts about getting to nurse wake her up.
I could have written your post. In fact, I came online this morning to write this post!!!
I did try sleeping in my older DD's bed so that DH could try to soothe DD1 and get her back to sleep without seeing me. That woke all of us and within five minutes every time DH was in DD1's room WITH the screaming 2yo telling me I was needed. This happened 5+ times a night!!! Poor DH does not have the stamina for night weaning!!
Here's what I'm trying: First, DH is *finally* starting to be able to put DD2 down for the night. He did it successfully a couple times. Now he's backsliding. He just gives up. If she's almost asleep and then re-wakes he's done, doesn't want to try any more and brings her out of the room, into a light, noisy room, to come get me. BUT I think he'll get better at that and in the process he'll learn that that can happen in the middle of the night too. I'm thinking of spending one evening a week in a local coffee shop. That way DD1 will know having me there isn't an option and, frankly, DH will know there's no back-up too.
Second, DD is good about understanding when I tell her just one more minute to nurse. So at night I've been saying that. Then I pop her off after a minute. She's been latched on pretty much all night recently so even this, even if I have to do it seven times a night (which happened last night), is a huge improvement and will get her used to sleeping without the nipple in her mouth.
Third, my 5yo many nights will go to sleep with a cd of music playing quietly in her room. It is one of the many tricks we've been trying to help her sleep. But I think that if I put the cd on repeat, and it plays all night, that might help with the screaming episodes. It isn't ideal, but hopefully this won't be a long process!!!
I'll be watching here for advice, too. I need any I can get. I'm desparate to get some real, uninterrupted sleep. Right now, even two hours of straight sleep sounds like an impossible luxury to me!!! I haven't had that in FIVE years (note issue that DD1 doesn't sleep well).