The transformation of elastic impedance (EI) from partial-angle-stacked seismic data is a crucial technique in the domains of reservoir modelling. Conventionally, EI inversion is performed on a per-angle basis, leading to significant discrepancies in EI values across different angles, which may not accurately represent actual conditions. When the signal-to-noise ratio (SNR) of seismic data is low, the inverted EI tends to be unstable, resulting in poor-quality inversion outcomes. This research proposes a novel method that allows for enabling the derivation of EI for various angles simultaneously inverted from multiple partial angle-stack seismic datasets in one process. The aim of simultaneous inversion is to potentially ensure consistent EI results. To obtain this aim, we utilize an advanced regularization method called the Gramian constraint. Consequently, the objective function for the simultaneous inversion of multiple EIs is developed. Results from both synthetic and field data demonstrate improved stability in EI inversion, especially for the case of low SNR.