Quantum well (QW) states formed in a double-barrier magnetic tunnel junction (DMTJ) enable the coherent resonant tunneling of electrons. This phenomenon is significant for both the fundamental understanding of quantum transport and the development of advanced functionalities in spintronic devices. Careful engineering of the structural and chemical disorders at the QW/barrier interface is essential to maintain strong electron phase coherence, thereby ensuring reliable conductance oscillations in DMTJ. In this study, we systematically investigate the influence of interfacial disorders and band structure on QW-induced conductance oscillations in epitaxial Fe/MgAlO_x/Fe (QW)/MgAlO_x/Co/ Fe DMTJs grown by molecular beam epitaxy. It is found that the amplitude of QW oscillations is reduced to one-third due to chemical disorders caused by the incorporation of 2-4 monolayers of Co at the Fe (QW)/MgAlO_x interface. In contrast, structural disorder induced by the incorporation of a single Fe monolayer completely suppresses the oscillations. In addition, the QW oscillation depends on the available majority Δ₁ states of the injecting electrons at the Fermi level (E F ) with k_// = 0 from the upper electrode. Replacing the Fe upper electrode with Fe₄N, which lacks a majority of Δ₁ states at E_F, significantly reduces the oscillation amplitude. Instead, using the bcc Co upper electrode, which possesses majority Δ₁ states, results in no change in QW oscillation. Our findings highlight the critical role of interfacial disorder and band structure in QW-induced conductance oscillations, advancing the development of spin-dependent quantum resonant tunneling applications.