Hi All,
                I am using a vf page which overrides custom object,Object__A is parent to Object__C and Object__B and Object__A is child to some other object ex:Object__P ,I am overriding Standard New button of Object__C with vf page,Now my requirement is when I select Lookup field Object__A i want to auto populate some fields of Object__A and its parent Object__P and child Object__B fields  also.
Note:   Object__C has no relation with Object__P and Object__B,it has only relation with Object__A.
   This is an urgent requirement ,please help me to achieve this requirement.
  Thank you.