Yes, the JioPhone does have FM radio. In fact, it is wireless FM radio. You do not require to use the earphones to use the fm radio.
Yes, JioPhone does have the NFC sensor.
It does take about 2 hours time to fully charge the JioPhone's 2000 mAh battery.
Yes, you can use Airtel sim card in the JioPhone but the Airtel sim card will work only on 2G network.