They are not meant to be shared. In their paper Fare Guide, it notes that a One Day Convenience Pass is "Valid for 8 trips on Bus, Subway, Trolley, in one day by one person". And because the pass has to be punched by the operator, it's not easy to "share" it.

If you're planning on using the bus/subway/trolley for no more than 4 trips each, tokens are cheapest. (You can buy them in packs of 2)

If you're planning on using the bus/subway/trolley for 5 to 8 trips each, the One Day Convenience Pass is cheapest.

If you're planning on using the bus/subway/trolley for 9 or more trips each OR plan on using ANY part of the regional rail system, you MUST buy a One Day Independence Pass. (Or pay very steep prices)

Note that the easiest/quickest way to get from the airport to downtown is Regional Rail.

Hope that helps!