[lelio]

My engineer brother-in-law came over and told us that our phone was at a frequency to high for a normal 'bought at RadioShack' scanner to pick up, so it may be a police scanner.
What he probably means is that you have a 2.4GHz phones, which came on the scene a couple of years ago. The old ones were 900MHz which any scanner could easily pick up. Sales of scanners that pick up 2.4GHz are banned in the US (in each scanner there's a chip that allows you to go around that frequency, but not listen to it), but you can pick them up in Canada or over the internet.
But that's bucks ($800+) and if they can't pay their rent I doubt if they are buying scanners. Well unless they have a need for it.
We have the exact opposite problem here: person rented out his house to some clowns that blast music at all hours, constantly are drunk, etc. So far it looks like he hasn't done anything to correct the problem. But based on your experience I doubt if he can do anything.
How about setting up a video camera to record the goings on? Dollars to doughnuts you'll catch them doing something illegal that you can show the cops.

[mlmr]

But that's bucks ($800+) and if they can't pay their rent I doubt if they are buying scanners. Well unless they have a need for it.

People of this calibar do not necessarily "buy" their appliances. The scanner is probably hot.