The amplitude for emission of n photons with polarizations $\epsilon_{\mu_j}$ written as $\epsilon_{\mu_1}\ldots \epsilon_{\mu_n}\mathcal{M}^{\mu_1 \ldots \mu_n}$ satisfies $k_{\mu_1} \mathcal{M}^{\mu_1 \ldots \mu_n} = k_{\mu_2} \mathcal{M}^{\mu_1 \ldots \mu_n} = \ldots =0$ due to gauge invariance (do you know this fact? This is a consequence of ward identity for abelian gauge symmetry)

For your process of two photon emission $\mathcal{M}^{\mu_1 \mu_2}\equiv A^{\mu_1 \mu_2}+\tilde{A}^{\mu_1 \mu_2}$. So it should become clear

The amplitude for emission of n photons with polarizations $\epsilon_{\mu_j}$ written as $\epsilon_{\mu_1}\ldots \epsilon_{\mu_n}\mathcal{M}^{\mu_1 \ldots \mu_n}$ satisfies $k_{\mu_1} \mathcal{M}^{\mu_1 \ldots \mu_n} = k_{\mu_2} \mathcal{M}^{\mu_1 \ldots \mu_n} = \ldots =0$ due to gauge invariance (do you know this fact? This is a consequence of ward identity & abelian gauge symmetry)

For your process of two photon emission $\mathcal{M}^{\mu_1 \mu_2}\equiv A^{\mu_1 \mu_2}+\tilde{A}^{\mu_1 \mu_2}$. So it should become clear

The amplitude for emission of n photons with polarizations $\epsilon_{\mu_j}$ written as $\epsilon_{\mu_1}\ldots \epsilon_{\mu_n}\mathcal{M}^{\mu_1 \ldots \mu_n}$ satisfies $k_{\mu_1} \mathcal{M}^{\mu_1 \ldots \mu_n} = k_{\mu_2} \mathcal{M}^{\mu_1 \ldots \mu_n} = \ldots =0$ due to gauge invariance (do you know this fact?)

For your process of two photon emission $\mathcal{M}^{\mu_1 \mu_2}\equiv A^{\mu_1 \mu_2}+\tilde{A}^{\mu_1 \mu_2}$. So it should become clear

The amplitude for emission of n photons with polarizations $\epsilon_{\mu_j}$ written as $\epsilon_{\mu_1}\ldots \epsilon_{\mu_n}\mathcal{M}^{\mu_1 \ldots \mu_n}$ satisfies $k_{\mu_1} \mathcal{M}^{\mu_1 \ldots \mu_n} = k_{\mu_2} \mathcal{M}^{\mu_1 \ldots \mu_n} = \ldots =0$ due to gauge invariance (do you know this fact? This is a consequence of ward identity for abelian gauge symmetry)

For your process of two photon emission $\mathcal{M}^{\mu_1 \mu_2}\equiv A^{\mu_1 \mu_2}+\tilde{A}^{\mu_1 \mu_2}$. So it should become clear