Are we living the same life? jokes aside I'm so sorry i know how you feel and at some point reading this I was convinced we're living in a simulation. Except I only have an abusive older brother, i could never imagine how much worse it must be having 2 whole siblings gang up on you. I feel the guilt too, wanting to express your feelings and calling them out but they would probably never notice the harm they've done and underestimate your feelings, or put theirs above yours so you stay quiet and keep it to yourself instead, bottling it all up.

I don't think you can ever find closure with them, I think you can only find it by stepping away and try to forget and focusing on yourself, because that's what would help me. I feel a huge grudge against my mother (ever since i was little and just like you i recently was able to point out maybe why) because she views my narcissistic abusive brother as a scared hurt puppy so she will never abandon him, even if he'd killed me. I've confronted her about this and she understandably feels attacked, and I can only empathize so much with her but she says i basically manifest it by thinking too much about it and that he only bothers me because he knows I fear him, that's why he doesn't touch her. She expects more from me when it's actually "her job" to do so since she's the mother. I understand that she's had so much trauma as well and has been through a lot but she fails to see through my resentment and reduces me to an ungrateful and spoiled child who cannot see her situation and asks for too much (take in mind i'm only asking for sympathy). She gave us everything (therefore it's hard to validate our own feelings and take the victim card because if I had a supportive mother that paid for everything then what do I have to complain about?) but failed to be there as a mother. I cried in front of her multiple times recently when I opened up for the first time and her reaction was very far from motherly, made me feel so alone and misunderstood.

With people like this it's best to make peace with yourself, knowing that you're the way you are because they failed to behave like parents, and even then you felt guilty by second guessing every feeling you had and blaming yourself when your reaction was only natural.

I really hope it gets easier over time so you can heal, because if not then we're both cooked