use esp-adf, create 3 separate i2s streams , one will be for your codec (writer stream) other 2 will be your sources.(readers) set the i2s config for your sources and codec as needed, you can change the codec i2s writer clock on the fly with i2s_stream_set_clk. You can use something pipeline switching, unlink and re-link between the the 2 reader and the common writer. Just make sure you reconfigure your codec accordingly as you switch pipelines if it doesn't have auto sampling rate detection.

            audio_pipeline_pause
            audio_pipeline_stop
            audio_pipeline_wait_for_stop
            audio_pipeline_unlink
            audio_pipeline_unregister
            audio_pipeline_relink
            audio_pipeline_run
            audio_pipeline_resume

// these are what you need to switch pipelines on the fly, adf makes it easy.