I did it!! But I'm not sure if I can explain HOW I did it! I've tried so many things that they kind of run together. But this is how I THINK it went:
I went into "Edit Town" and there I removed the whole family from the game. That puts them on the clipboard. THEN you separate them, and put each group back in the game (or not) as you like. I put my new family back in their old house, and sent the separated couple to a new residence.
I'm very happy this worked, as I had set up a game with the two I wanted out in a tiny room in the cellar with no door, as a last resort. I thought I could starve them to death and remove them that way. Horrible, I know, but I was out of ideas. Then I realized the woman was pregnant! Well, that ended that experiment. I just couldn't bring myself to murder a baby. The whole idea of this made me incredibly uncomfortable, even now, just writing about it! I know they are not real, and each time I delete a game I'm "killing" characters, but it's not the same.
So, if you're still having problems getting your Sims to move, try taking them right out of the game and putting them back. It worked for me! Good luck.
Phyrie