How agencies and clients work
An agency account composes; client (company) accounts send. Each client has its own HubSpot portal, sender and branding. The agency invites a client, the client accepts (or the agency creates the account), and from then on the agency can assign campaigns, flows and hubs to it.
Distribute, don't duplicate: the agency keeps one copy; each client gets a live assignment that resolves to the client's own sender, branding and portal at send time.