We have tried to give a self-consistent explanation of isospin mixing and Fermi beta decays for 54 <= Z <= 68 deformed nuclei. The effect of isospin impurity in nuclear ground states on Fermi beta transitions has been investigated considering the restoration of symmetry violations stemming from the mean field approximation. The isobar analogue excitations in neighbor odd-odd nuclei have been obtained by following the proton-neutron quasiparticle random phase approximation (pnQRPA) procedure. The dependence of isospin admixture probability on the deformation parameter has been determined for various isotopes of Z = 54-68 nuclei. Then the variations of isobar analogue state energies and the beta decay log(ft) values with deformation parameter have been calculated for the same nuclei. Thus, the influences of the isospin symmetry violations on Fermi transitions can be clearly understood.