You need to configure Azure File Sync to meet the file sharing requirements.

Sync groups: 3. Storage Sync Services: 1.

In Azure File Sync, a sync group defines a single sync topology and can contain exactly one cloud endpoint (one Azure file share) but can contain multiple server endpoints (on-premises server locations) that all sync to that same file share. Fabrikam needs newyorkfiles to sync only to FS1, seattlefiles to sync only to FS2, and companyfiles to sync to both FS1 and FS2. Because each Azure file share can only belong to one sync group, newyorkfiles requires its own sync group with a single server endpoint on FS1, seattlefiles requires its own sync group with a single server endpoint on FS2, and companyfiles requires a third sync group whose one cloud endpoint (companyfiles) has two server endpoints, one on FS1 and one on FS2, which Azure File Sync fully supports within a single sync group. That gives a minimum of three sync groups. A Storage Sync Service is the top-level Azure resource that contains and manages sync groups, and there is no requirement here that forces the shares into separate Storage Sync Service instances (such as differing regions or subscriptions); a single Storage Sync Service can hold all three sync groups. Therefore only one Storage Sync Service is required.