Restrictions for choice on Primary point of contact picker, when a user raise a Service Request

Summary:

We would need to restrict employees to restrict the choice on primary point of contact ALL users including higher roles e.g. Mangers, Executive Directors etc.

Specifically, we need to know how to restrict this: 

a) Restricting a group of employees for which it is possible to choose only according to the organigram (e.g. people of the same Team/Unit) 

b) Applying some automatism able to read the organigram so that an employee is forced to choose as primary point of contact only colleagues from the same Team/Unit

Thank you,

Regards