Dear ,
Dual reporting normally arises when the employee is working in some regional/branch office and his departmental head is in Head office. In this case his administrative reporting would be to the location/region/branch head and functional reporting would be to the department head. If your case is same, then you need to decide prior hand in consultation with the HR Head and management about the weightage to be given to the reporting heads. As a standard norm, the functional head should be given more weightage and hence you can keep 75%+25% mix of the feedbacks received from the heads. It is always good to set different set of questionnaire. For administrative head , you can keep questionnaire related to behaviour (major) and functional (kra linked- minor) and for functional head, behaviour (minor) and functional (kra linked-major).
But if your case is different means having two reporting boss in the same department , the feedback should be taken from department's head only. And in case the employee has reporting to department's head and director, then you need to consider both but more weightage should be given to department's head ,after all for performance of the department, heads are responsible.
This is a suggestion only when you don't have any set of policies on that. However it is always good to formulate some policies regarding the authority/power of heads/reporting bosses in case of dual reporting , if numbers of cases are there like this.
Also as per your first query, the parameters for termination/promotion etc etc....can't be defined by us. It is your management who will decide the parameters as every business has different set of objectives. So talk to them and formulate policies accordingly.
Hope this will be helpful. ..