No they don’t. You can invite them to your Space, and they’ll be able to sign up for a Blinkist account of their own to join the Space.
If you have a Blinkist Business account: anyone within your organization can invite or join a Space created by another colleague within your organization, they can simply create an account upon creating/joining a Space if they haven’t already. You won't be able to invite someone with a personal Blinkist-Premium account to a Space you created with your Blinkist Business account.