A five-step phase shift demodulation scheme based on a multiwavelength averaging method is proposed to suppress crosstalk within an extrinsic Fabry-Perot interferometric (EFPI) sensor array. The paper focuses on a two-element sensing system based on the EFPI sensors to investigate the crosstalk in the EFPI sensor array. A detailed theoretical analysis of crosstalk suppression using the proposed demodulation method is presented. Numerical simulations and experiments are put forward to demonstrate the effectiveness of the proposed demodulation scheme in suppressing crosstalk under varying parameters. The results of the multiwavelength demodulation scheme indicate superior crosstalk suppression capability in contrast to the conventional five-step phase shift demodulation scheme based on a single-wavelength demodulation method. Furthermore, the paper reveals the enhanced crosstalk suppression capability of the proposed demodulation scheme when the cavity length difference between elements is not equal to zero. It alleviates the requirement for consistent cavity length among different elements in the sensing array. The proposed demodulation scheme exhibits excellent crosstalk suppression capabilities in optical multiplexing arrays by decreasing the dependency on extinction ratio and could be potentially used in the large-scale optical hydrophone array system.