Does sound like a difficult situation to be stuck in the middle of. Home for three years unemployed certainly cannot be good for his self esteem, yet, it's on his shoulders to rectify that, as a responsible adult. I once worked for my states unemployment department during the first recession of the millennium. Similar happened to the same demographic. Many had to switch industries, sometimes settle for less than where they were, but a paycheck was better than no paycheck.
As far as your mom, granted it's tough being the sole breadwinner coming home to walk on a whole bunch of eggshells, but it's also up to her to put herself first, and deal headon with her marriage and decisions. Gently nudging her to a therapist, may help?

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