The process is similar to the creation of option 2 audits, as seen here in the relevant recordings.
Therefore, in this scenario as well, you need to create a parent site "PG/Multisite scope information (Site)" and assign all products of the option 1 multisite with QMS to this parent site.
When creating the audit, you need to select the option "Option 1 - Certification Scope Management multisite with QMS" as seen here:
The QMS audit needs to be created with "Option 1 multisite with QMS" as seen here:
The sampling audits need to be created with "Option 1 - Site of Multisite with QMS":
