This may be a bit too elementary question for this site but is it possible to control SQL Server authenticated logins using groups? So is it possible to assign sql logins under groups and give rigths for these groups? If so, are these groups only seen for an instance in question?
When working with SQL Logins you "group" them by using roles within SQL Server. Roles are created at the database-level but with SQL Server 2012 you will be able to create them at the server-level as well.
Once the role is created you can assign specific permissions to that group and it will be applied to the logins that are member of that role. The roles are localized to the instance you are under and are not visible or accessible to remote instances. You will only be able to add the logins in that instance of SQL Server to the roles.