Have a customer that wants his Apple Music and his wifes on the Sonos app. How is this done?
TIA

Add Apple Music to Sonos
iOS or Android

Open the Sonos app.

From the Settings tab, tap Services & Voice.

Under Music & Content, tap Add a Service.

Tap Apple Music, then tap Add to Sonos.

Follow the on-screen instructions to add Apple Music to Sonos.

Taken directly from Sonos' website.
Google is your friend.

Does she/he not have their own phone or tablet? You create your own Sonos account on your device and log into your services. Those service will play to the SONOS system when you use 'your' Sonos app on 'your' device.

Just like when a guest comes over with their phone and has the Sonos app, wanting to use your SONOS system to play 'their' music thru.

Husband adds apple music service through their phone and syncs it with his apple music account on his phone

Wife adds apple music service through her phone and syncs it with her apple music account on her phone.

Just note that they may need to re-sync their accounts from time to time if it hasn't been used for a while.