If you want each member in the team to be listed as contributor you all need a account each.
Then when one of you upload it you can add the other users as Admins to the game.
Check this thread for detailed instructions: https://itch.io/jam/open-jam-2018/topic/312173/how-do-i-add-a-collaborator-to-a-submitted-project
Hope that helps anyone confused! :)