I'm not seeing a better way to work out the parent/child relationship so I've done this kludgy method. You could adopt the same principle in your code.
If the comment doesn't have an ancestor then it must be a top level comment
Then use the Replies.Count to iterate through the replies
Code:
Sub aTest()
Dim aCmt As Comment, sAuth As String, sReplies As String
Dim i As Integer, aReply As Comment
For Each aCmt In ActiveDocument.Comments
If aCmt.Ancestor Is Nothing Then 'a top level comment
Debug.Print aCmt.Author, aCmt.Done, aCmt.Range.Text, aCmt.Replies.Count
If aCmt.Replies.Count > 0 Then
For i = 1 To aCmt.Replies.Count
Set aReply = aCmt.Replies(i)
sReplies = sReplies & vbTab & aReply.Author & ": " & aReply.Range.Text & vbCr
Next i
Debug.Print sReplies
sReplies = ""
End If
End If
Next aCmt
End Sub