Does each teammember need to sign up individually or do we need to signup with only 1 account?

Once the 48h submission window is open, you will be able to submit a game that you uploaded to itch.io. Uploading the exact same project by each team member is a bad idea, as it would most probably be deemed as spam.

I'd recommend that your entire team register for the jam just in case of technical difficulties. And once your game is ready, one of you can upload and submit it.

Thank you Ktosox, it is all clear to us now

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! :)