Explanation
Each site in an organization must have a unique name and URL. You cannot have two sites with the same name or URL in the same organization.
ReferencesAdd a new product to your organization Update a product URL to a new URL

Explanation
Currently, you can only create one sandbox for each linked product1. Since you have only two products (Jira Software and Confluence), and you already have a sandbox for Confluence, you cannot create any more sandboxes for your organization.
References: Manage product sandboxes

Explanation
When you copy data from production to a sandbox, the user permissions and groups are also copied. This means that project admins from production can access and manage the same projects in the sandbox. However, customers and agents from production cannot log into the same portals or projects in the sandbox, because we disable app links, external email notifications, and integrations with Bitbucket and Slack. Attachments and comments are also not copied to the sandbox, unless you choose to copy with media files.
References = Manage product sandboxes, Copy data to sandbox

Explanation
The groups jira-software-users-acme and jira-admins-acme are default groups that are automatically created when you invite users to Jira Software or assign them the Jira admin role in your organization. The suffix acme indicates that the groups belong to the organization with the domain name acme.com. The groups are used to manage product accessand permissions for Jira Software, but they do not imply anything about Confluence access or org admin privileges. Therefore, the only statement that is definitely true is that your organization has the Jira Software product.
References :
Default groups and permissions
Users & Permissions | Jira Software.

Explanation
If Ann's email domain is not verified by your organization, it means that you do not own or manage her account. However, she may have a managed account in another organization that has verified her domain. In that case, you cannot enforce security policies, deactivate, or delete her account12.
References:
Verify a domain to manage accounts
Solved: Verify domain - Missing accounts