There has been a lot posted on Apple forums about iPhone 4S WiFi problems since the update iOS 7. So far I have updated two iPhone 4S's and an iPad 2 to iOS 7 and have not experienced any problems. I am not sure how you have been updating the devices but I updated all my devices to iOS 7 via iTunes not the downloaded update on the device. I did this in order to have a full backup of the device on my PC. The funny thing is, every one of these devices had a slight glitch during the update process that required me to restore the device from my computer backup as part of the update process (the way it used to be done). That may very well have cleared or avoided whatever had been causing problems. I know that Apple often recommends a backup and restore when devices start acting up. The only suggesting I can make at the moment is to take one of the malfunctioning devices and try a full backup and restore via iTunes.
I support the right to keep and arm bears.