What I'm about to say is not backed up by any official statistics or scientific research or whatever, just my personal experiences. Oftentimes, it's the elders themselves who are responsible for the abuse within their own homes, whether that abuse is physical, mental, or emotional. Of course this does not apply to all elders, but for the ones it does apply to, they should not be in romantic relationships, and they should not become fathers. They are complete and utter morons, emboldened to be abusive not only by the standard nonsense that all JWs are subjected to, but also by all of the extracurricular indoctrination designed only for them.
They are basically taught that anyone who is not an elder is beneath them, and they don't respect personal boundaries. They are taught that it's perfectly fine to sit in a small room with a woman, interrogating her about what kind of panties she had on when she fooled around, whether or not she shaved her groin, how many times she orgasmed, what positions were used, and if she enjoyed it. I once heard an elder on stage address all of the sisters in attendance, and he said that no matter what the elders ask, they should answer. He even went on to relate how some sisters actually have the nerve to get offended when certain questions are asked, and said that an uncooperative attitude should be avoided. Fuck him. I wanted to go up and use the edge of the stage to curb stomp his goddamn teeth out.
If a brother has any tendencies toward toxic masculinity, then becoming an elder will likely bring out the worst of his personality. Of course there is nothing wrong with being masculine, but there are just certain aspects of it that must be kept in check. I try to remind myself of that every day. I would recommend that you encourage this person to do secular research on narcissism and abuse, to talk to a professional counselor, and last but not least, to leave the fucknut that they joined in unholy matrimony, and start living a real life.