It is possible that unchecking the File Sharing option might help the overheating situation if the temperature sensors inside the AirPort Extreme are being fooled by a "bug" in the AirPort firmware.
Unfortunately, it is much more likely that the overheating messages are being generated as a result of an internal fan that is clogged with dust. This occurs quite often in AirPorts that are 12-18 months old or older when the fan cannot produce enough airflow to keep the internal electronics inside the AirPort at a normal operating temperature.
If you continue to see the "overheating" messages, there are really no shortcuts or easy fixes at this point. If you have AppleCare in effect on one of your Macs......and.....the AirPort is less than 3 years old, Apple will usually replace the AirPort for you under the AppleCare coverage.
If the AirPort is no longer covered by warranty......and.....you want to continue using the AirPort, then the only option at that point is to open up the AirPort and replace the fan. This is not a tough job if you are good do-it-yourself type person. The links below provide more details on this:
AirPort Extreme A1521 Fan Replacement - iFixit Repair Guidehttps://www.ifixit.com/Guide/AirPort+Extreme+A1521+Fan+Replacement/19553
CPU Fan For Apple Airport Extreme A1470 A1521 ME177 ME918 MG60121V1-C01U-S9A$9.96eBayNo tax
