rittz,
If by equal construction you mean equal material and thickness (which would mean that their rigidity per unit length is the same) then yes, the shear at each shearwall would be proportional to their lengths.
In order for the interior shearwall to be effective, you would need to provide a collector element though, to transfer the forces from one side of the diaphragm to the shearwall.
In terms of the tension in the boundary chord, it would certainly be different with the interior wall. Your diaphragm would basically be a inifinitely stiff beam supported by springs (the shearwalls), each with it's specific k value. The span moments resulting from this idealization must be divided by the lever arm of the boundary chords (in your case least dimension of builiding) to obtain the boundary chord forces(T = M/d).
Don't forget the oversrength factor when designing the boundary chord elements, as well as the diaphragm collector and it's connection to the shearwall.