Hello Barnabas
If you are configuring a single cloud scenario, then yes, you will need there to be a link between the primary hub and both secondary hubs. The two secondary hubs act as “clients” of the primary hub and require a connection. However, you only need to create a link between each secondary hub and the primary hub.
Now if you’re implementing the dual cloud scenario, you won’t need to explicitly create a tunnel between the hubs like you do in the previous scenario, because in this case, the secondary hubs are not clients of the primary hub. Each hub is configured independently.
I hope this has been helpful!
Laz