flight PARIS TOKYO via SHANGHAI GOING 2h15 TRANSIT , return flight 20H transit in shanghai

sorry its not clear to me where, who and how i get this 72h free transit. we are a couple holding both french passports:
1. for the going flight, for the 2h15min spent in transit in Shanghai, do we need a visa?
2. if we need a visa, and we take it from the airport Shanghai, do we have enough time 2H15min?
3. for the return flight, we need to obtain another 72H twov?
4. do we have the right to go out of the airport with this twov and enjoy the city, sleep in a hotel, and return next day for the final flight?
thank you in advence