I don't have an answer but I have some questions that might help point the way, or at least point away from some answers.
Why do they specifically want electronic doorbells? Is the house built in such a way that all three of any doorbell can be heard from anywhere in the house? Or will they need to have some kind of repeater or doubling up of doorbells?
Aiphone or some other type of intercom/doorbell system might have multiple sounds.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
