I wouldnt worry to much about the transition. My kids did great when it came time to change them around. First my son and daughter shared the upstairs room, as my son was a little nervous about going downstairs, then when my second daughter was born, he was moved downstairs without a hitch, he got a nightlight and new beddings and all was great. When we got pregnant for the fourth time, we had to move our daughter downstairs with my son, and it worked out just fine, she loved the new place. My other daughter switched out the crib quite nicely, as she wanted a big bed like the others anyways. When the babies are older, they will move downstairs too, and I am confident that since they love being with the older ones and have to do things all the same, it will be an easy move too. Good Luck!