There is a sentence in my english book:
Jonathan Hill mentions that it is not unusual for certain details to be difficult to obtain from family members.
My teacher says this is incorrect, it should be to be difficult to be obtained because it's not the details which obtain. However I think it's correct the way it's written, because the 'to be' applies to the structure 'difficult to obtain', not just to 'difficult'.
Is the first one correct or not?