I couldn’t find clear answers for setting up Sonos with Amazon Music Unlimited HD Family Plan and Alexa. So, wanted to share what we did in case it is helpful for others.

Our system is: 

• Sonos One in the office
• Sonos One in my daughter’s room
• Stereo pair of Sonos One SLs with Sonos Subwoofer in the living room 
• One phone with Sonos app and Alexa app to control everything (daughter doesn’t have a phone)

Our goal:

• Connect Sonos to our Family Plan
• Play music from separate accounts in the Family Plan for myself and my daughter
• Have Alexa recognize our voices and by default play from the correct account in the Family Plan

Required steps:

1. Create the Family Plan on Amazon (in our case, we were upgrading an existing account to a Family Plan)
2. Invite family members to join the account on Amazon. As far as I can figure out, these accounts must be adult accounts. Teen accounts cannot be added in later steps to the Sonos system. When you are in the Sonos app and try to “Add a Service” using a Teen account, the authorization process fails because Teen accounts are not allowed to log into Amazon from any apps.
3. Have the family members accept the invitation and complete the process of being added to the Amazon Family Plan.
4. In the Sonos app, you need to add each account as a music service. Go to Settings → Music & Content → Add a service → Amazon Music→ Add to Sonos → I already have an account. Follow instructions to add the family member. Repeat this process for each family member. 
5. In the Sonos app, define the music service that will be the default for that device. This will have been set already so you may not need to make any changes. Go to Settings → Music & Content. Click on the account that will be the default account for the app. Click Use on This Device.
6. In the Alexa app, log in to the account for which you want to have a voice profile. Create a voice profile for that user: click on the hamburger menu at top left corner of screen, then Settings ->Your Profile → Voice. Follow the instructions. Repeat this process for each user. If you are managing all of this from one phone / device then you need to logout, log in as the new user, and go from there.
7. You can set preferences for Alexa for each user e.g. prohibit explicit music lyrics. Log into the Alexa app, click on the hamburger menu at top left corner of screen, then click on Settings. There are a bunch of preference topics in the list. (Explicit lyrics is under “music & podcasts,” voice purchasing is controlled under “Account Settings”)
8. And that seems to do the trick...

Results:

• Alexa recognizes our voices, accesses correct playlists, and records music history to the right accounts.
• You can check which profile Alexa is using by asking, “Alexa, which profile am I using?”
• You can force the profile that Alexa uses by saying, “Alexa, use profile for oname].” 

Limits:

• You cannot use Amazon Teen accounts. Not ideal for kids but you can work around by 1) not giving the kids the password to their Amazon accounts, and 2) turning off “voice purchases” in each Alexa profile just in case.
• Songs played via Alexa are not added to the song history in the Sonos app. 
• As far as I can tell, you cannot set up Alexa to only control the room it is in. If you say “Alexa, pause por stop or off]” when you do not have music playing in that room, Alexa will stop the music in whatever room has music playing, This makes sense -- Alexa looks for a logical thing to do with the command. However, it’s a problem when kids are yelling at Alexa in another room. Our experience is that they give extra commands and keep turning off the music where I am listening.
• I can’t figure out how to use Alexa to control the music in multiple rooms. I can tell it to “pause in uroom]” or “play louder in sroom]” and those work well. However if I am listening to a song in one room and I say “play in room 2]” then Alexa starts whatever was paused in that room, rather than adding that room to what is currently playing. Similary, if music is playing in another room I can’t get Alexa to move it or add it to the room I am in. 

Hope that helps.

J