Determine first if the Macs can even get a hint of the wireless network with a program such as iStumbler. Find someplace with a working internet connection to download iStumbler and copy it to a USB stick:
This will at least let you know if your Mac can even see the network. If it can't it may be the hardware is losing its signal. Note there is a range within a WiFi access point where overlapping waves are too strong and cancel each other out too closed to the access point. The best range is between 5 feet and 150 feet direct line of sight. File cabinets and piping can interfere with this.