My SIL is using my brother as a wallet

I think my (39F) brother (50M) is in an abusive relationship. They have been together for ten years but have a LDR for 6 of them.
Whenever she (51F) visits she milks him dry of money and always demands the best and most expensive experiences. She expects him to drop everything he is doing and cater to her.
Example: we moved to a different country, she shows up after three weeks, mind you he was not working at the time, she demanded to be driven around and taken to see places. When I tried to explain we just moved and don’t know the area yet, she did not care. She started to complain about and to my brother, and it’s hard to watch when she berates him for littlest things. She even berated him for not cooking. When I explained the cooker in the new flat is different and because he is near sited he can’t see the controls for the cooker, she went off about how a 50 year old man can’t even cook a meal.
When he visits in our home country, he spends two months wages on her ‘demands’. Even pays off any debts she got into. (He even paid to build a new house, it’s in her name only btw, the excuse was for tax reasons)
I didn’t say anything up to this moment as they see each other very really and I don’t see them interact that often, but when I do hear it or see it. It’s really difficult to hold my tongue.
I’m afraid if I say anything I will just strain my relationship with my brother, I’m at a bit of a loss how to talk to him about it without damage.

TL;DR my brother is in an financially abusive relationship and I don’t know how to approach this without straining our relationship.