If you open System Preferences on one of your Macs, click on Wi-Fi on the left, then unlock (in the bottom left), and then click on Advanced... in the bottom right. It will then list all the Wireless networks that have been added to that Mac.
In this case it sounds like these networks have been previously added, therefore when the Mac is turned on it will try auto-connecting to them again.
You should first delete them from the list, and secondly consider turning off the 'Remember networks this computer has joined' to prevent them being added again.
If these other networks belong to someone else you cannot hide them or disable them, and in many countries jamming them would be illegal and interfere with your own Wi-Fi as well.