Or two or three or more... I have friends in abusive marriages. They know and they don't know. Coercion, financial abuse, sexual abuse (just short of rape), constant belittling, gaslighting, criticism, semi threats of violence. There are young children. No one has come to physical harm so far. It might never. All the light has gone from my beautiful, kind, intelligent friends. I really can't go into detail as it's too outing.
All the advice online is to tread carefully, listen, don't label anything as abuse and just try to redirect back to them how they're feeling and what they say has been done to them. But this has been decades now, I think it's affecting the children, and my heart breaks for all of them.
YABU - It's impossible. Telling people to leave their partners will only result in them shrinking away from you and further isolating themselves. Every single piece of professional advice says that people have to realise these things for themselves.
YANBU - Tell them what's what because the soft approach hasn't worked.
Obviously, all I want to do is the latter, but i just worry it will backfire horribly and then I won't be welcome, and they'll need me for when things get worse.