I have the account, and previously my wife set herself up as a member of the same household in my Prime account. So, have you ever done this; it might help.
Anyway we currently have both our phone numbers in our Alexa apps. When testing, I left a voice message for myself via a Dot, and it indicated it was from her. My cell phone rang and also all the Alexa gadgets did too. I answered either via my phone or another Dot. It all appeared to be working fine.