Firebase.util.NormalizedCollection merge multiple paths

Question

I would like to know if it is possible with Firebase.util.NormalizedCollection to merge 3 paths or more who depends on each other. On firebase doc it said that the best practice with our datas is to have flattened data as possible, so I have that :

question : 
    uniqueIdqestion1 : 
        myquestion : "ma question",
        answers : {
            uniqueIdanswer1 : true,
            uniqueIdanswer54 : true
        }
answer :
    uniqueIdanswer1 : 
        my_answer : "my answer",
        people : {
            uniqueIdpeople1 : true
        }
people
    uniqueIdpeople1 : 
        name : "pedra"

With Firebase.util.NormalizedCollection, I would like to list all the answer for my question and have an array like that :

key_answer : uniqueIdanswer,
my_answer : "ma response",
name : "pedra"

I tried to have something like that with this code :

  var ref = firebase.database().ref();
  var nc = new firebase.util.NormalizedCollection(
      ref.child('questions/' + $state.params.chatId + '/answers'),
      [ref.child('answers'), 'widget2'], // B path
      ... ???                            // C path

  )
  .select('widget2.my_answer', ???).ref();
  $scope.reponses = $firebaseArray(nc);

But I can't still understand how to merge the B and C path. Maybe it's because C doesn't refer directly to the main path, I don't understand because something is missing for me in my mind ... Please can you help me with that ?