1, yes. I'm in a very remote location. 2, mostly yes. Others use the WiFi, but no one else would even know how to reach the router config page and make such a change, nor would they really want to.
When this happened to me, I found the router completely reset itself - like the configuration information got corrupted and it decided to reload the settings from scratch. It was hidden inside a cupboard and the only thing was a power outage that happened that appeared to scramble the memory. Because after resetting all the settings, it was fine.
Router is 8-9 years old now. Sounds like its slowly dying.
Might be able to save it with some dd-WRT that won't help with the aging WIFI-G limit of the hardware. Unless money is priority, I suggest a new router.