I don't tell my parents anything and they have absolutely no business in any part of my healing/recovery, so if I come across as a bit aloof here, sorry. I don't understand having relationships like this or wanting support from parents. That being said, it sounds to me like you are not 100% sure what happened but want validation from them. If you don't even know for sure, they have a right to not feel sure either. It's a pretty big deal. But ideally they'd support you in your need to uncover truth and heal, in however that works. If it feels like they can't do that, leave them out of it.
Do you feel like you need closure on the pieces of memories or images? Have they naturally fit themselves together or are you putting them together to create a memory? I'm NOT saying you are making up sexual abuse. I'm wondering how the not-sures are forming into memories. I do understand all the fuzziness around early memories. I do know for sure, and remember pretty well, some early medical trauma, physical abuse, and sexual assault. The fuzzy memories involve images, some feelings, and memories of really odd behavior on my part... and I don't know who or if anyone hurt me but have had a nightmare of my mom molesting me. Other indicators might point there too. There is just super likely SOMETHING. When I was assaulted I felt re-triggered, mysteriously, and tried to kill myself a few days later.
But that's in no way something i'm willing to string pieces together and say what happened (I will not tell anyone that I think my mom molested me because the reality sucks too much and the pieces aren't perfectly there...and I feel no need to dig or figure this out). There is so much garbled information in my mind. I focus on my current symptoms. I have meltdowns over physical pain or feeling like it's hard to breathe. I hurt myself. I also don't connect with others. This could all be from my known traumas. But basically I'm just focusing on managing all of this better....and as I do that some of my trauma starts to make more sense (I have connected some of my worst feelings of immobilization to very early body memories).
Aside from telling your parents about suspected abuse, do they know you are in therapy? Are they supportive otherwise? I believe this feels invalidating but I wonder if they read that you aren't sure and personally don't believe it could have happened and also sense safer for you to not believe that too. That's not saying disbelieve reality. But I'm not sure, in what you write, if you are sure this happened and I wonder if your parents are also working around reading that off of you...and maybe even meaning to be supportive, even if it feels like invalidation? Not sure I'm saying what I mean. Feel free to disregard if confusing or unhelpful.