At the end of the movie Thir13en Ghosts, is Cyrus a ghost or a real person? If he's a ghost, why can he be seen without the glasses?
That's the point. Arthur taking off the glasses while Cyrus still stays visible shows that Cyrus wasn't a ghost at all. You seem to forget that Cyrus planned all this in advance. He wasn't dead at all and this whole story of him inheriting his house to his nephew was just a setup to get Arthur and his family into the house, since he needed Arthur and his love for his children as a final key to drive the machine.
All Cyrus wanted was the machine (which the whole house was) to work in order to use the powers of the Ocularis Infernum to his advantage (see comments) and for this he needed somebody sacrificing himself out of true love, which he couldn't do, but fortunately he knew somebody that could, Arthur. So he lured him into his house by faking his death and coming up with that heritage plot.