security issue

 1- For security issue, we need to force developers and application functional consultants to login with their own login credentials and not sysadmin user .In other words we need to create a login credentials for each developer/consultant with his own username/password. This login should have the same privileges as for the sysadmin user. Can you please advise how we can accomplish this?

2- All Developers are currently using the apps user to access the db. We want to :
a) Create other logins with different with the same privileges of the apps user.
b) Create different logins with only query and execute packages privileges.