I just figured this out... it was very a very frustrating issue. Here’s the fix:
Step 1) Open the Home App on the main account that setup the HomePod device.
Step 2) Go to the house icon in the top left hand corner.
Step 3) Navigate to the bottom of that list and click on “Home Settings”
Step 4) Touch on the person in your household you would like to have be able to receive notifications, etc. (if not there, invite and have them accept the invite to join the home). Note: Make sure the individual has enabled location services to “While Using” for the Home App under Settings / Privacy / Location Services / Home
Step 5) Enable “Add and Edit Accessories”
Step 6) Hit “Back” and “Done”!
Step 7) On their device, go into Home App
Step 8) Navigate to the HomePod and long touch.
Step 9) Swipe up till you open settings (or click the gear).
Step 10) Select Intercom and turn on appropriate settings.