The recent discovery of superconductivity in the multilayer Ruddlesden–Popper nickelates La3Ni2O7 and La4Ni3O10 has raised fundamental questions about its underlying mechanism. A central issue is the connection to the density wave transition observed in both materials, which exhibit notable similarities alongside key distinctions. Elucidating the origin of this density wave is thus essential for identifying the pairing mechanism. Here, we present a comprehensive study combining pump–probe resonant elastic x-ray scattering and x-ray absorption spectroscopy to investigate the density wave transition. Our results provide new insight into the coupled electronic and spin degrees of freedom and their role in superconducting pairing.