This depends on the user license type. Talend sales should explain this to you. But the concurrent license type allows you to use so many users at one time. So, if you have 5 concurrent users, you can have 100 users but only 5 logged in at a time. If you have 5 named users (license), then you can only have 5 users set up on the TAC. I guess you could, in theory, share 1 license amongst a load of users in both scenarios. With a concurrent user you could set up 10 users and only use 1 at a time. With a named user you could just share that user name and password....but only one developer at a time.
