If you are using the Divvy App, each user account can rent only one bike. So if you're with someone, they need to download the app as well.
However, if you want to rent up to four bikes with one credit card, use the kiosk.
Remember: wherever you buy your Explorer Pass from (app or kiosk) is what you should use for new ride codes while your pass is active. You cannot buy an Explorer Pass from the kiosk and then get a new ride code from the Divvy app.