The geometry of conformal minimal two-spheres immersed in G(2,6;R) is studied in this paper by harmonic maps. Then in most cases, we determine the linearly full reducible conformal minimal immersions from S^2 to G(2,8;R) identified with the complex hyperquadric Q_6. We also give some examples, up to an isometry of G(2,8;R), in which none of the spheres are congruent, with the same Gaussian curvature.