In this paper, we propose a coexistence scheme based on orthogonal frequency division multiplexing (OFDM) and affine frequency division multiplexing (AFDM) to enable efficient joint sensing and communication (JSAC) under different channel conditions. Specifically, the distinct signal representations of both waveforms in the frequency and affine domains are exploited to ensure the orthogonality and flexibility of the proposed mechanism. Furthermore, a novel pilot design is introduced to enable joint channel estimation for both communication and sensing tasks. To further enhance the scheme's adaptability, the proposed approach dynamically responds to channel mobility, ensuring seamless operation in JSAC networks. Numerical results validate the effectiveness of the design, demonstrating accurate low-complexity radar parameter estimation while maintaining high data rates, as well as reducing the peak-to-average-power ratio (PAPR) compared with the conventional OFDM and AFDM.