Glad I asked.
Here's a little more info:
Some of our moves have been extended ordeals, so we broke down and got a second wireless router for those times we're shutting between houses. In another five weeks, we'll finally be in a solitary two-story rental.
I looked into whether it's possible to use one router as a repeater, for better range. Turns out people do it.
I already have all the Cat 5 and tools, if that ends up being necessary. And buying something else would be possible, if it's a lot easier. Wireless repeater, wireless access point, etc. I'll take a look.