J.G.
Hi G.,
I feel your pain and frustration! When my two oldest were younger I had a calendar in the then 4 year old's room and we marked days when she didn't get up to wake me up. so many days equaled some type of reward. Start small so that the reward is fast coming. Did your kids share a room at the old house? Do you think your 2.5 year old would sleep better in a big boy bed. My middle child didn't sleep through the night until we took her out of her crib and put her in a big bed. Could you put them each in their own room?
Also, I took a parenting class when my kids were 4 and 2. One suggesstions was for mommy and daddy to have quiet time (15 minutes or so) alone without interruption sometime when the children could see you and know what you were doing. "couch time" is what it was called. The theory was if the kids know mommy and daddy are okay, good relationship, etc., then they feel safe, don't need to see them together in the middle of the night. I really think this helped us at the time we were experiencing extreme sleep deprivation.
Good luck! It can be done - I have finally gotten all three of mine sleeping through the night in a new house in the same room! My 1.5 year old when through a nasty waking period but right now we are good!!