Organization/Individual Contact relationship
afaik there is nothing in civicrm that delivers quite what you ask. 

The closest 'in the box' is probably the 'contact dashboard' which does let Primary Contact edit the Organisation record, and if you "allow second degree relationship permissions" here the if Primary Contact has permission over the ORganisation and the Organisation has permissioned relationship over the other employees, then Primary contact can edit those people.

Of course the Primary Contact needs a joomla record to login to do this