Jeffee, if this reply is not too late for you I would suggest that with a complex multi surface design of that sort that you make up an all balsa or all thin foam test glider and play around with the CG location. Ideally the rear set of lifting surfaces would be adjustable in angle compared to the forward surface set to play with CG vs decalage angles (as in front set to rear set in this case, not the classic biplane upper to lower wing angles) to find the critical rearward point where the CG and related trim angle between front and rear surfaces still provides a proper recover from a slight stall. But just barely. That would be your most rearward CG location for the proper model.
With something of the sort you cannot rely on the usual CG calculations. They just do not provide for all the interactions of a total of 6 flying surfaces like a test glider would do.