Currently a single Zapier account can be linked to a Hubspot account.
This means that it is impossible for multiple Hubspot users with different permissions to use Zapier. Merging all the Zapier accounts is often not an option as it breaks the principle of least priviledge (https://en.wikipedia.org/wiki/Principle_of_least_privilege), which is particularly important to respect when dealing with sensitive data such as customer data.