I don't have the numbers on them, but as far as I know, they are rare. The most discovered so far were five planets with shared barycenters.
Take a look at the orrery though, because based on the system map, I think you're a bit mistaken. It looks like bodies 2 and 3 orbit each other - a binary pair of gas giants, and 4 and 5 also orbit each other - a binary pair of a gas giant and a planet - and these two binary pairs also orbit each other. A binary of two binaries, if you will. Yours is quite nicely symmetrical.
You can compare with other examples posted in
this thread.
Oh, and congrats on your find!