I have to agree with you L, he was way to calm. Most youngsters would have screamed, yelled, or what ever and run away probably dropping what they were holding at the time. Plus if your sister had said to you that something was finishing her jigsaws at night, you would have teased her and told your parents about it. NOT pick up a camera phone and do some paranormal investingation and try and video it. Why does the shadow go round him not through him? It is not natural for anyone to come out of a bedroom and slide down the banister to go down the landing.
Thats just my thoughts though.