Hey Bek,
We are going through this now with Ivy. You have my every sympathy.
I have both Ivy and Noah in the room together now to train them to a big bed. It was too hard having one in one room and the other somewhere else. So you can imagine the mucking around that goes on! What I did with the other kids and what I am doing witht his pair is to have the normal sleep routines and after I tuck them both in, I sit between the beds with a book. If they muck around or get up I just get up put them back into bed and tell them it's time for sleep. Ivy and Noah have been sharing now for just over a week and I am starting to see that they are settling better. I think you are doing the right thing by pushing through it. It might take a little while but you(and she) will get there well before your next baby is welcomed into the household!