iCloud+ share custom email between two accounts?

I have setup a custom email domain on iCloud+, for myself and my spouse. We currently have the accounts 1. {my name}@{custom domain}, associated with my iCloud account, and 2. {spouse's name}@{custom domain}, associated with their iCloud account. We also want to setup something like {family}@{custom domain} (accessible by both iCloud accounts!) for certain accounts that we want easy joint access to. Is there a way to do this? I see how to associate such an account with solely my iCloud account, or solely theirs, but not both of ours.