Not sure what the primary issue is, searching forums will reveal multiple instances and explanations of using CBSubs for two different profile types. The following is an ideal scenario, but this is simply 1 of the many formats and use cases you can use.
Parent: Registered - Free
Child: Employer - Exclusive, No Upgrade
Child: Employee - Exclusive, No Upgrade
Edit the employer and employee plans accordingly to restrict what parts of the site you want them to have access to.
If say a user is fired, delete them. The user count for your license is based off the total records in the users table, "fired" or not they will count against your license limit; if you expect many numbers you should purchase a higher limit license.
As far as employers passing off the account, they simply need give the login access to the new employer at which point the new employer should change their password.