Each person needs one. Pasmo/Suica is read when touching the IC card reader upon entering and exiting a gate, and the correct fare is deducted from the card. The same card cannot be read entering twice at the same station.

No, two people cannot use the same Suica card simultaneously for train or bus travel in Japan. The Suica system (as well as PASMO and ICOCA) works on a "tap-in, tap-out" logic to calculate the distance-based fare. If you tap in and then try to hand the card back to a second person to tap in again, the gate will sound an alarm or display an error because the card is already registered as being "inside" the station. Every traveler, including children (who have their own "Child Suica" for half-price fares), must have their own individual card. This applies to both physical cards and mobile Suica on iPhones or Android devices. However, you can use the same Suica card for multiple people in a retail setting, such as at a convenience store, vending machine, or restaurant that accepts IC payments, as these are simply flat-rate transactions. For transit, ensure every member of your group has their own card or a paper ticket to avoid bottlenecks at the ticket gates.