AFAIK, none of them are "BuiltIn accounts".
They are probably accounts created by someone in your organization.
If you want to know if they are still in use, you could look at some attributes on those accounts.
In Active Directory Users and Computers (dsa.msc)
- Click on View and make sure that "Advanced Features" is checked
- Double click on the user account
- Click on Attribute Editor tab
Look at those attributes and you will know if they are still in use:
The date will show you the last time the account was logged, has changed or the password has changed.
Another way would be to make a common query
in the same console (dsa.msc)
Right click on your Domain and click on Find...
Click on the Find drop down menu and click on "Common Queries"
Click the drop down menu beside "Days since last logon:" and select a value
Click on Find Now
you will have the list of all users that has not logged on since the number of days you have chosen.