  In this work, we study the lepton-number-violating processes of $K^\pm$ and
$D^\pm$ mesons. Two quasi-degenerate sterile neutrinos are assumed to induce
such processes. Different with the case where only one sterile neutrino
involves, here, the CP phases of the mixing parameters could give sizable
contribution. This, in turn, would affect the absolute values of the mixing
parameters determined by the experimental upper limits of the branching
fractions. A general function which express the difference of the mixing
parameters for two-generation and one-generation is presented. Special cases
with specific relations of the parameters are discussed. Besides, we also
thoroughly investigate the CP violation effect of such processes. It is shown
that generally $\mathcal A_{CP}$ is a function of the sterile neutrino mass.
