Excitations and enhanced coupling at the magnetic metal-insulator transition in NaOsO3 and Cd2Os2O7

5d oxides provide new paradigms of cooperative interactions that drive novel emergent behavior. This is exemplified in the osmates NaOsO$_3$ and Cd$_2$Os$_2$O$_7$ that host MITs where magnetic order appears intimately entwined. However, unlike the iridates where spin-orbit coupling (SOC) behavior dominates, in the 5d$^3$ osmates an orbital singlet is expected and reduced effect of SOC. We measure the inelastic spectra with neutrons and RIXS. Our results uncover the 5d-manifold splitting to reveal a suppressed role of SOC in the creation of the electronic ground state but dominant behavior in the creation of the magnetic state. Moreover at the MIT in NaOsO$_3$ we find a giant spin-phonon coupling and in Cd$_2$Os$_2$O$_7$ a magnetic excitation corresponding to a superposition of multiple spin-flips.