I'd go for therapy @MissingYellowzigzags not because there's anything wrong with you, but so that you can talk it out and be validated.
I went to therapy about 3 years ago because my mum was so hurtful to me. So hurtful and so defensive. When I asked her to stop glossing over decades of projection (various labels such as paranoid) she turned it all around, attacked me, became the victim of me, gave me the silent treatement, smeared me, blamed me, ultimately, rejected me (I've been written out) so even though I didn't believe that there was anything fundamentally wrong with me, I went to therapy. It was very validating which was what I needed. Just to be reassured that to be hurt is the normal logical predictable reaction to hurtful behaviour. I wanted the therapist to make me invincible but she validated my reaction and my hurt. She helped me get a bit of distance from the pain, but like your main question poses, how do you ever find complete acceptance of such an injustice.
My mother is in her 70s too so I cant help thinking it's all very short sighted of them (sibling included). I did love them. I would have helped where I could (without losing my job). At the moment my mum is so completely enabled by my Dad that if she's not speaking to me, he's not speaking to me, ykwim. If she's the victim of me, he gets to be the rescuer. It's all so dysfunctional.
Therapy did help a lot. It's not a magic wand, it doesn't make the issue go away but honestly, if you've been going over there three times a week, treat yourself to one session of local therapy and then if you feel up to it, go over.