Hi @JuanDaniel
You can certainly shared an account but as you mentioned, each user having its own account is the way to go.
When it comes to the WORK library, it will be assigned to the session and not shared by your three users (if they use the same account).
For your last question, there isn't a way to achieve what you want but versioning might be what you're looking for. Might.
If you have questions about versioning, many if not all will be answered with Paper 179 - 2014 Check It Out! Versioning in SAS® Enterprise Guide®.
Hope that helps.
Cheers,
Damo