Active Directory Tool

Implement a cleanup tool such as
https://www.experts-exchange.com/articles/30820/Active-Directory-Cleanup-Tool-ADCleanup.html

There are a number of tools out there such as ADManager (which I use at my job) or UMRA.

For reporting part, You can try my AD reporting tool - AD FastReporter Free.
There you can easily find user accounts whose password is set to never change and computers/users who haven't logged on for a period of 3 months or more.

You can easily locate Active Directory accounts with passwords set to Never Expire:
https://community.spiceworks.com/how_to/128015-how-to-locate-active-directory-accounts-with-passwords-set-to-never-expire

There are tools to do such task easily like; Lepide and Managengine.

Hope this helps!