The JFETs in the schematic snippets are working in different roles, analog switch, rectifier diode, some possibly as buffer.
Generally, it's quite difficult to analyze the exact function of similar circuits "bottom-up", without knowing the overall function and involved waveforms, even with a good foundation in analog circuit design. The circuit analysis must be at least supported by a "top-down" approach, identifying the principle function of each block and the related signal pathes.
We have seen a large numbers of similar schematics in previous Edaboard threads, e.g. from former member danny davis. In my view, it was rarely possible to get much insights.