WIBTAH if I (anonymously) report my partner's siblings due to their misdemeanors?
Note: Some details are omitted/mixed up to avoid being doxxed as some involved individuals are active here in Reddit.
I (3*F) have been with my partner (3*M) for 10 years. At the inception of our relationship, I was severely harassed by his narcissistic parents and oldest sister, who even targeted me with death threats and libelous rumors because my family did not meet their "social status." I filed for police blotter report but didn't press any charges. Throughout this ordeal, my partner and his 3 other siblings defended and protected me. 6 years later, I climbed the corporate ladder, built a small business, and became financially successful, and now his parents suddenly "accepted" me with no apologies or discussions, as if nothing ever happened before. I have moved on (and set some distance) and just embodied "l forgive but don't forget"+ "out of sight, out of mind" mindset for my peace.
My partner has essentially cut ties with his family (since the aforementioned ordeal) and only speaks to them transactionally about their business, assets, properties, etc. Now, we're about to get married. For the sake of taking the high road a.k.a not divulging internal rifts, the parents and oldest sister are invited but they will not play any significant part on our wedding nor they're given any platform to do anything but unfortunately will "need" the sibling to be part of entourage to avoid unnecessary drama and another fight it might come to.
While planning our wedding entourage, I discovered that this same oldest sister committed serious misdemeanors that violate their community's rules. I cannot disclose what the community is but it's highly political with mix of business and "religion" in. I aired out my apprehensions to my partner of including his sister in our entourage due to what I've found out; I'm not even part of their community but I myself became uncomfortable knowing these. My partner has reported it, but it has become apparent that his parents covered it up to protect their ~highly-regarded reputation~ as they will be ostracized (or worse, be removed from their community) as a result. This is entirely hypocritical, as they are usually the first to report others for the exact same behavior.
2 weeks ago, this sibling had done something again and it basically escalated. I asked him why he isn't reporting again, to which he answered, "I will not waste any amount of effort to please or displease them because I don't care anymore, they're narcissists, and l've done more than enough of even inviting them." I asked how he would feel if I reported it anonymously, and he said I be the judge of that, as long as it doesn't disrupt our peace and has assured me that he will always have my back.
For context: we're Asian, but I grew up on a westernized upbringing while my partner and his family are on a traditional/conservative setting.
WIBTAH if I anonymously report his sibling?