I ran into a similar stuff after my mom died. My sisters and I could grieve honestly. I can't really be honest with my aunt and dad. It also just didn't feel right to dredge up the ugliness with them anyway. Like I'd be beating them when they were down or something.
It was helpful for me to acknowledge that what I was grieving for was what will now never be. I kind of knew, long ago, that my mom would never have the proverbial "come to Jesus" moment about her actions, but it didn't really hit home until after she died. The finality of that was what made me sad about my mom's passing. There's not really a lot of people you can explain that to, in my experience. My friends and church people were giving the usual condolences and would ask me how I was doing - even months later. It was jarring.. Especially when someone would first explained how hard it was dealing with their beloved mother's death and they understood. (???) It felt awkward and heartless after that to say, "I don't really miss my mom." KWIM?
Just remember, being honest about someone's actions is not unforgiving.