The (isospin-mirror) radiative nucleon captures, Li7(n,photon)Li8 and Be7(p,photon)B8, are subjects of long-standing interest for astrophysics. The Li8(B8) nucleus can be considered as a shallow neutron+Li7 core and neutron+Li7* (proton+Be7 core and proton+Be7*) p-wave bound state. Li7* and Be7* are the core excitations. The scattering and bound states can be studied in Halo-Effective-Field-Theory (Halo-EFT) framework. The couplings in the EFT Lagrangian are not known a priori and are difficult to extract from experiment. They can, however, be obtained from QMC calculations of the Li8 and B8 nuclei. In our leading order calculation, we use asymptotic normalization coefficients from QMC calculations to fix the EFT parameters, and then apply the theory to study radiative capture reactions. Our results for both captures compare favorably with available data, within the estimated theoretical uncertainty. I will emphasize the important role of proton-Be7 scattering parameters in determining the energy dependence of the cross section (S factor), and demonstrate that their present uncertainties significantly limit attempts to extrapolate data to stellar energies.