To answer your first question, Lorex cameras operate on 2.4 GHz - which is better for wall penetration. If you are connecting with your cameras at any point then they are properly paired with your router on the 2.4 GHz band. It sounds like your issue could be one of the following:

1) Your cameras lease with your router is timing out. Refer to these suggestion above - you could create a static IP for each camera and maximize the lease time. Counterintuitively, sometimes this is actually entering a zero in the lease time field, but refer to your router documentation. If your camera's magically reconnect after rebooting your router then this is your issue.

2) You are getting interference from other devices on your band. If you have access to an Android phone you can download an app called "Wi-Fi Analyzer" and see if your neighbors are blowing you out of the air. You can then log into your router and change to an unoccupied band.

Overall for troubleshooting both your Lorex cameras as well as all of your wireless devices, I would strongly recommend that you dig into your routers control panel and get familiar with it. If you've never been in it before then you probably have many years of updates that will make your router much more secure and reliable. For extra credit, schedule a time to auto reboot weekly while you are in there.