As many other people have noted in their reviews, this is an extremely frustrating site. Technically speaking, you can't really "visit" as it is privately owned and not open to the public.
I tried pulling all the strings I could with the Brussels and Flanders Tourism boards (I'm a travel photographer) and there was nothing they could do.
As far as I know only one group has been allowed in, in the last decade, and they were friends of the owners.
What is especially frustrating is that the facade of the structure doesn't even face the street. What you can see is actually the back of the house.
From everything I have read, the interior of the building is stunning and it is really worthy of world heritage status. Until the family can come to some sort of resolution, we have to wait visit this fine building.