I don't know how you determine who has what characters, and I don't need to know, but my wife and I are grouped in as the same player, so we're maxxed to 3 characters between us. I'm fine with the two characters that I have, but she would like to play more than one. When she tried to make a second character, it said "You already have three characters." I don't know if there's any way to resolve this, but we really enjoy the game, and would like to both enjoy the full experience.
While I agree that the bonuses are good for donating, and I would love to donate in the future, our current funds do not allow for it. Maybe later in the month, after bills are all paid. Not sure how it would work for us, though, as the bonuses are applied via same email, and she used a different email than I did to create the characters. The character limit has been fixed, thanks to Tim, and we are playing together. We've even started a new clan, "Airach", "The Living".