So, I decided to get the new Proudspire Manor addition to see what it's like. After buying it from Falk Firebeard I went back to the house, but I couldn't for the life of me figure out where the new room was supposed to be. Eventually I noticed a glitchy flickering wall by the main bedroom, and when I walked up to it I saw the tooltip "open door". By using the "tcl" command I was able to see that the whole childrens' room was there, but the original wall where its door has been added is still there! So the room is inaccessible without cheats and all I get from it is an ugly, glitched out wall. Has anyone else seen this and/or have any idea how to fix it?

Yes. I have this exact problem. I bought the children's room extension and then found a a shimmering door next to my bedroom in Proudspire. There is no option to open the door. I am not well versed in console commands, but I would appreciate any solution people can suggest.