How to setup Cross Business Group?

 Hi All,

   Recently our client brought 2 subsidiary company (B & C) under them. We implemented Oracle HRMS and Finance for the parent company (A). And now we are planing to implement the same for subsidiary company(B & C). For subsidiary company ( B & C) ,  a staff in subsidiary company (B) can be  a supervisor of an employee in subsidiary company (C), but a staff in parent company (A) cannot/shouldn't  be  a supervisor of  any employee  of subsidiary company's ( B & C). How this can be achieved?

Note 1 : We cannot set the Cross business Group to 'Yes' at site level due to some Financial setup and it has to be 'No' at site level. And I can see that, for cross business group profile  at the responsibility level , it's not updatable .