Looks like it'll fly. Just get the CG right.
The Hercules flying wing from CrashtestHobby.com used an elevator in the middle and had two elevons.
You will most likely find that it will fly the best if you have a little reflex set up on all three surfaces.
The Obelix is a 20+ year old slope glider design. Back then elevon mixing was either mechanical or super expensive!
I actually built one of these but never flew it. The success of the design comes from putting the elevator and vertical stabs back away from the CoG so that they have a decent moment (i.e. lever effect). The incidence of the body wing to the outer wings is also key to the stability (which is achieved on conventional flying wings with reflex).