With much respect, what experience do you have with Stockholm syndrome? It is massive abuse and yet they are convinced that they can't live without this person and defend their abuser. It is deeply sick and unhealthy behavior in which they have convinced themselves they are happy. There is no discussion with "the partner" that will ever bring about anything. The abuser is a control freak and is not capable of rational thought (think psychopath). And the abused are constantly convincing themselves this is true deep love and nothing is wrong and they are happy, they will not seek out therapy. They will occasionally admit things aren't perfect, and these are the conversations I have with them - not started by me - by them.
Do you understand the bond that occurs in abusive relationships? The more abusive, the stronger the bond even. Do you understand they lies they tell themselves to make the behavior of the abuser "okay?" Do you understand there is dissociation and brain washing involved? And I don't even particularly start the rational conversation, they will start it but then the dissociation kicks in. They are struggling on the inside but can't admit it.
So, you are suggesting that I should give up and stop having relationships with my brother, my business partner and my friend? The relationship they have with the controlling women is affecting my relationship with them.
Yesterday, I had a completely rational nice conversation with one of them. We did hit a little bump when started telling me how I should approach something at work which I completely disagreed with and he had ulterior motives for wanting me to approach it his way. I did not bring up the ulterior motive, knowing it would cause friction (and it was coming from the controlling woman who was behind it). I just stated that it didn't make sense and I would do it my way, and reminded him that he didn't like it when I told him what to do. Then we discussed other projects we had been working on and he told me that I could no longer be a part of them. First he lied and said that he never said that I could. Then he just said not to question his judgement (this again was the woman controlling him that was blocking me from projects I have been working with him on for years). Again I refrained from bringing up the real cause and said that I would go find projects elsewhere (despite numerous years of work). He then got mad at me and told me that he shouldn't be involved with me at all and that I was telling him what to do and what to think (none of which was said, and I challenged him to scroll through our conversation - it was a chat - and to find where I had done any of that). He is doing me wrong, knows it and yet has to do what his controlling woman says. This creates huge discord in himself and becomes completely irrational, makes up stories in his head to justify his actions. He is trying to control me, to please his controller and is feeling guilty about it all at the same time.
With much respect, interfering in the relationships of others brings nothing but trouble. You can be there as a sounding board (or not, if it gets to be too much to handle) but I might consider refraining from "having rational conversations" with them so that they can "see the light". If they are unhappy, the person that they should be having a conversation with is their partner or a therapist.