There should be a global friends list separate from the wizard-based one. This global list can be accessed by all wizards on your account. Additionally, when you add a wizard to your global friends list, you will add every single wizard on their account, but collectively each wizard will only take up one slot, so you are effectively adding someone's account but not exactly. Furthermore there would be an option to press a button by someone's name on your global list to see the rest of their wizards.
In addition to this update 2 elixirs should be ibtroduced, one for expanding your wizard friend list and one for expanding your global one.
I think this is a good idea because if you want to add the same people on all of your wizards, it's gonna take a lot of time, and not to mention it's annoying. Thanks for that suggestion!