Not sure if I can help, but I am in the same boat almost exactly (except I only have one). My son is 14 monts and I am going to start trying to get pregnant in April. I just started nightweaning -- well that's misleading because I have been sort of trying for months, but just started in earnest. I'm not sure if this will work if you exclusively co-sleep, but we use a combination crib and bed. Basically, I breastfeed him at about 7:30 p.m. Then I either give him to DP to get down and put in his crib, or I do it (if he doesn't fall asleep nursing I rock him or do whatever it takes). Once he is in his crib I try to keep him there until at least midnight or 1:00 (by rocking or patting him back to sleep if he wakes). He has only recently started giving me 3-4 hour stretches to start. Then, the new part: the first time I bring him to bed I do NOT breastfeed him. It usually only takes him about 5 minutes of fussing while I rub his back or hold him to fall asleep, especially because he has already been asleep. We are now up to 7-9 hours with NO NURSING, for the past several nights. I'm crossing my fingers I'm on to something. Good luck and I hope you find a solution soon.