➀ The project owner can invite other team members to the project and set up individual access permissions for every team member.
➁ Some features of the project owner's subscription plan are available to invited members for free:

The default access: 

View posts and stories.

By permission access:

Editing posts and stories.
Project management.
Management of project members.
Instagram account management.

Not available:

Office tools: bio profile, ideas, templates, hashtags features.

➂ If the project owner's subscription is inactive, then the invited member's access to the project will also be inactivated.