Some options to consider:
Look for SmartApps that natively support multiple temperature sensors like [RELEASE] 5-2 Day Programmable Thermostat Scheduler (Weekday, Weekend) with Remote Temperature Sensor for each Schedule) or [RELEASE] Motion Sensor Thermostat Detect Presence Based Temperature but that assumes that the apps provide the functionality that you’re looking to achieve.
If you’re using a custom app then one option may be to modify the app to support multiple sensors and then average them.
If it’s a simple routine/action that you’re trying to use based on average temperatures, you can also create the action using WebCoRE or CoRE.
You can also check out ActionTiles to see if they can create a tile to average sensors for display purposes.