obs running on the nas would mean that if the pc crashes the stream doesn't go down with it.
though you would need to configure the main pc to stream to the nas and then have it restream to the desired endpoints. That would be the simplest thing though the least flexible.
OR do the proper stream pc setup and add a video input card to the nas, and a bunch of other things like controlling obs, camera and mic input etc. And have the nas do all the compositing and mixing and then streaming it all.