a. This is not available out of the box in C360, but you can configure a field in customer info/relationship object and populate the field via rules engine.More information on how to set this up can be found here.
b. This can in turn be used in Fields to be added in Relationship widget in 360 in the card/list view and viewed in C360. For each of the relationship associated with the account, the NPS score will now be visible in C360.