
I figured it out this weekend.
Take Rob's huge collection of T-shirts out of the smaller closet by my side of the bed in our bedroom (New Office) and put them...um...somewhere. I've already emptied out the dresser in there of my things, discarding some of the contents and squeezing the rest into two other dressers in our bedroom. I'll try to convince him to cull the collection, but he bought many of them at science fiction conventions and so considers them souvenirs, which means he must hold onto them until he dies. And then he'll expect his heirs to hold onto them forever, too. Convincing him will be very uphill work. The argument that he doesn't need fifty to sixty T-shirts will probably fall upon deaf ears.
Take the stuff out of the closet in Old Office/Fiona's new bedroom and put it...um...somewhere. (Second closet in Rob's and my bedroom? Basement?)
Take dresser out of New Office and put it into the closet of Old Office/Fiona's bedroom. It will now be her clothing dresser. Her old dresser will remain in the old bedroom, now Delia's room. We don't have room to move her old dresser from her old bedroom into the New Bedroom with the desk there.
Take low green bookcase out of girls bedroom/Delia's room and put it into New Office. Fill it with books from my office, bookcases 1 and 2 and 3.
Take bookcase 1 out of Old Office and put it into Delia's room where the low green bookcase used to be.
Move arm chair out of Old Office into Delia's room.
Take Fiona's bed out of the girls old bedroom/Delia's Room and put in her new bedroom/Old office. Move bookcase 2 to a different position so that it's flush up against the bed. Fiona puts her books into bookcase 2 and 3, as well as leaving some in her old bedroom.
The only things I'll have to buy: a shelf for putting my computer on in the New Office, a chair, and a light source/lamp.