AITA for asking my cousin if our father sexually abused him?

I (38F) recently found legal documents from a 1990s child sexual abuse investigation involving my dad while helping my mother pack up the family home. My father has Alzheimer's and is in a care home.

The documents alleged sexual abuse against my father involving multiple children in our family. They included medical evidence that my sister "Amy" had been sexually abused, witnesses, and documentation that my other sister "Jen" and I had disclosed abuse at age 4. The medical evidence was detailed and disturbing. The case was eventually dismissed.

Amy, Jen, and I have always had fragmented memories and behavioral signs that something happened, but never had proof until now. We've been searching for answers about our childhood for decades.

When I told my sister "Beth" what I'd found, she revealed that years ago, she saw an email from our cousin "Dan" to our father that said something like "I remember what you did to me and I forgive you." Years later she asked our dad about it, he denied the email ever existed.

This seemed like important independent corroboration of a pattern separate from the legal documents I'd found. I sent Dan a message believing what Beth told me was true, told him I believed him, and asking if he'd be willing to talk to me about his experience. I also shared information about allegations from another family member.

Dan denied sending the email and was upset I contacted him. Now most of my family is angry at me. Beth has blocked me for violating her confidence, and says I ruined her relationship with our family. Multiple family members say I had no right to ask Dan about potential trauma, that I could have triggered him, it's inappropriate and I crossed a serious boundary. Jen says it's unfair to investigate while Dad has Alzheimer's and "can't defend himself". The only one who supports me is Amy, who is also the only one besides me who actually read the documents.

I'm really not sure if I did anything wrong here. I was acting on specific information I was told about my father's pattern of abuse, which directly relates to understanding what happened to Amy, Jen and I. I reached out privately and respectfully. Dan had the right to decline.

I acknowledge I should have asked Beth's permission first before contacting Dan, and maybe I should have asked Dan more neutrally rather than assuming Beth's account was accurate. But honestly, if I'd asked Beth first, she would have stopped me and I would never have gotten answers. I think if it's true, I have every right to know. If it's not true, Dan should know this is being said.

I thought I had the right to ask, but everyone says I was wrong. AITA?