When can I specify the team members?
Does every member of the future team has to join the jam? 

Thanks for they reply 🕹😁

If you had some team members, add them as admins to the submission, you can do that by:

• Click on 'Edit Game' on your game page
• Click on 'More' › 'Admins'
• Enter the username of your team member(s) 
• Click the "Show Contributor" checkbox for all team members