Define Bonuses, the stats like initiative/crit/injury work from every single ninja. The thing you level up with pills, like 30% nin and resistance only works from the one ninja equiped.

As for best cards, Tenten 20% crit to any ninja, works in every team, Rasa 20% def/res to any ninja who have a shield good if you using like GNW Madara with breaks. There is also a card which does bonus damage to all immune ninjas (forgot name) which can be nice now because many people use immune move 1 but imo Tenten is still better because Injury is such a op stat, difference between crit and non crit is huge.