It is not possible to have several different users connected to the same car/cars. Husband and Wife do not have the option to log in with their own email and see the same car in the app.
If the husband is set up for a car that is his and the wife's shared car and the wife wants access from her own phone to view the car's information, then the husband must give his wife his username (the email address he was created with) and his password to the app.
The wife then simply goes to GooglePlay or AppStore and download the Minxx / mitXX app and log in with the husband's user information.
This will allow them both access to the same car.
An alternative could to create a fictitious e-mail account (email@example.com) and use that for both users.