I come from a large family and there is quite a spectrum in terms of what types of abuse we all suffered. Some of my siblings are completely turned off emotionally, get uncomfortable when the horrors of our childhood are brought up, defend our parents to some degree, appear to have really unsatisfying relationships and be unhappy. For these siblings, I relate to them in an almost acquaintance like way, I want to have a relationship with them but I know that their emotional capacity is limited so I don't "go there" in terms of insisting they accept me "as I am" because I know they aren't able to process that. Because I want to have a relationship with them, I meet them where they are at.
Other siblings have dealt with addictions, unstable relationships and have received some therapy and other help. For these siblings, I have a closer and more honest relationship because they are aware that we had abusive parents. Also, I at times have to set limits in what they ask of me both emotionally and for one of them, financially. Because we had no boundaries growing up, I understand that they don't always know when they are asking for too much so I have to be firm with them sometimes in order to protect myself. The third category of sibling is one who is buddy buddy with my parents, thinks you should forget about the past and that we had a normal childhood. Unsurprisingly I have the least contact with them because they are really in fantasy land. They suffered less abuse but their childhood was still abusive and neglectful
Then there is me, I always looked like I was doing well from the outside but was dealing with PTSD, depression and addictions on the inside- completely turned off emotionally and acting my way through life. I actually think it matters very little how it looks like you are doing from the outside, sometimes the inner world of someone who has experienced severe trauma is way worse than one who looks like they are a train wreck. I spent years going to a highly stressful, life or death job and had constant thoughts of suicide and was emotionally turned off. By the grace of god I didn't harm anyone. I'm not even religious, I am just amazed that I was able to function at all.
Bottom line is this. If you want to have a relationship with the siblings you are describing, you may have to meet them where they are at, with the limitations that they have. They sound like they aren't really capable of fully understanding what you all have gone through and may not ever be capable. Can you get the validation about what you have experienced in your childhood from other people? It sounds very frustrating for you to want them to accept the reality of what happened and how you are feeling when like you said, they just want to forget what happened.