I do think the wing between both fuselages is extra strong, because it carries the mission payload. I see no problems with some elastic movement (on any modern plane the wings flex in turbulence) as the tails are mostly dragged along.
There will be some roll-axis flexing, but I see no issue with that. The middle wing looks pretty stiff with respect to yaw-axis flexing and that would need some wing-box strengthening compared to a single fuselage aircraft.