How to support sister in law who has a controlling H?

[StartupRepair]

Dh's sister is very dear to me. I am concerned about her marriage as her husband seems very controlling. Not in an overt way but at every moment she is trying to anticipate what he might want. Lots of last minute changes of arrangements because he has made a different plan. I feel she is constantly anxious that he will be displeased and always trying to avert this. At a restaurant basically everyone's order is controlled by him. 'i don't think we need dessert' and we all politely fall in to keep the peace. She told me recently that she is not happy but would not consider leaving as fears a breakup would be too distressing for their DC. They are wealthy and on the surface have a lovely life. He engages a lot with the DC but on his terms. Lots of sport and hiking etc and pushing them with homework.
They have been expats for many years and have recently returned to our city. S-l -l was unable to work while away and has effectively lost her career. Her H never acknowledges this cost to her. They have moved country many times for his career. Every time she patiently settles the DC, organises the house and does everything to facilitate his career.
My question - is it better if we just go along, be friendly and polite to him, ignore any tension, roll with last minute changes in arrangements etc? Or is it better to quietly say to her that their relationship seems completely oppressive and uneven and she shouldn't have to tiptoe around his anxiety all the time?

If it were me, I'd be gently encouraging her and supporting her to find work, hobbies and friends for herself.

With that, her confidence will grow.

Over time, she'll know she can rely on you to help her achieve independence, whether that is within her marriage or as a single person.

It’s great that they have come back to your city. It sounds like she has been constantly isolated and held down by her DH. He’ll find it harder to do under your noses and she’ll have support from you and your DH should things become worse for her. I think @Gazelda is right - encourage her to build her life as it’s only from doing that that she’ll find strength to stand up to him. Some people (particularly women) believe that going into a marriage means doing as they’re told and it can be small realisations over years that lifts the fog and make you realise this is bullshit and you’re just as important as your partner. You sound like a very supportive SIL, just be there to gently point out to her his misdemeanours as they happen. Be gentle though, don’t overstep. It’s up to her to take action (whatever that involves) but her knowing that his behaviours are not normal/correct will help her fog to lift.

I would gently encourage her to find a new job and become independent.
The danger of telling her what you think about her DH is that you push her away or that she will be feeling ashamed to ask for help if she decides she needs it / wants to leave him. If anything stand up to him yourself if he’s being a dick to her or anyone else in your presence. That’s all you can do.
People will usually not leave an abusive relationship until they’re ready for it themselves, not because others say so and there’s often a huge amount of shame that the victim has internalized. Speaking from experience here. That’s why I would encourage her to become independent. It helps her to build self esteem and she will no longer need him to get by financially.