If I interpret your explanation, you have a CCD with 26 runs for two continuous factors and one categorical factor with two levels. I am unaware of this design.
You intend to model the response separately for each level of the categorical factor. Why not use a single model with interaction effects?
You should not use the CCD in this case. It is intended, like all of the classical RSM designs, for only continuous factors. Additionally, it is a large design that is not as efficient as the I-optimal custom design of the same size. The size of the CCD is dictated by the design method (composition), the the number of parameters in the full quadratic model, and the selected properties (orthogonal, rotatable). Custom design any combination of factor types, any combination of model terms, and I-optimality. The number of runs is up to you as you deem necessary.