Thanks a lot for the responses--the explanations fit what I'm seeing, and the solutions seem viable. (I'd been doing makeovers on them for a while, then started killing them, then just started getting annoyed). The door deletion is definitely something I'll consider, since I have a 9-apartment lot I want to use and I don't have 9 families I want to put in it--I'm sure that place is contributing to the problem.
You can't put nine families in it anyway - the maximum is four.