I JUST finished writing an e-mail about the sleep issue to a good friend in your same boat -- she is pregnant (due in late December, when her little boy will be 2.5 years old) with terrible morning sickness and is also co-sleeping, but is starting to feel the wear and tear and that her little boy needs to learn how to sleep on his own. Which is sort of where I am with my girls at this point -- we are still all in the same bed, but it can get really tricky when they wake each other up at night and then we are all up and cranky and I fear the whole thing is counterproductive as none of us gets great sleep as a result.
Mine do take sippies at night -- they are down to nursing during the evening only, once, and then a sippy in the middle of the night. Usually they wake up and drink their sippies and want to get very close to me (i.e. on top of me is preferable, which of course can cause some bickering). It can get pretty unmanageable. My feeling is that I need to move them into their beds in their room as gently as possible, knowing that they are getting into that 2-year-old drama time of their lives, but also that it is a real skill to learn to fall asleep and stay asleep, and that the kind of mothering you have provided so far, my friend Molly has provided, I have tried to provide, well, what is that really for unless they can use the comfort and sense of security they have achieved thus far (hopefully) to be OK with undergoing a change.
I am also against CIO (crying it out), though. Along the same lines as above, I/we have always tried to practice principles of patience, loving tolerance, and reassurance around them (even when at a boiling point inside and believe me, there can be quite a few of those on a bad day!). My solution, I think, will be either to start moving them to their beds when they have fallen asleep in ours and letting them come back when they wake up in the morning, or to work out a way for Tom to do a story time/bedtime where they may cry some but won't be alone and then need to lie down and go to sleep. Part of it separate from straight-on crying it out will be just their preference for sleeping with me/us, and that's the part where I just have to trust that between what we have provided and their tiredness level at the end of these days, they will learn it's OK to sleep in their daytime beds at night.
I will keep you posted. I do think that (and just old my friend this, too) if I were in your situation with a finite time until another baby and starting the whole process all over again existed, I would want to have a little bit of myself back and to share with my husband before undergoing the next one!