Explanation
There's a 1:1 relationship between an Azure AD Connect sync server and an Azure AD tenant. For each Azure AD tenant, you need one Azure AD Connect sync server installation.
Therefore, we need to deploy two servers that run Azure AD Connect for the two Azure AD tenants.
Each user account can only be synchronized to one Azure AD tenant. Therefore, we need a way of splitting the users between the two Azure AD tenants. Azure AD Connect offers three ways to filter which users get synchronized to an Azure AD tenant. You can use domain-based filtering if you have multiple domains in a forest, attribute-based filtering or OU-based filtering.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-topologies#multiple-azure-ad-tenan
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-configure-filtering