Register front end member from admin area with password
Your best bet here is going to be to create a plugin.

One way that this could work would be to set up a plugin that defines a record for the front-end users, and then create one or more Control Panel pages for your Administrator to handle these records. Because the records can be defined any way you'd like, they can exist separately from Craft's baked-in User system. 

This may actually be preferable in your case, since (if I'm understanding correctly) it sounds like you'd like to manage users logging into a separate frontend area, not the Craft admin Control Panel.

Regarding the Admin ability to manage User's passwords from the Control Panel, this feature was removed in build 2.3.2615. However, this answer does offer a way around this.