They say they will listen, have a family liaison officer assigned, etc,
They say that. I would be extremely surprised if that happened and if you didn't receive a response that was traumatic in its own right. Best case scenario they'll just talk to you like you're a time waster and suggest you get some counselling. Nothing meaningful will end up logged (might just be that you were distressed and referred to mental health services).
It is completely outrageous they won't ever be held accountable and that the truth won't be acknowledged. It's shit.
In the unlikely event you called the police or walked into a police station and they weren't dismissive dickheads to you, then you would be the one investigated primarily. Your history and medical records would be trawled through to find proof you're not credible (and being mentally ill with PTSD is not considered proof of credibility but to make you less credible).
You would go through video interviews where you would have to relive all your trauma in more excruciating detail than you probably imagined possible (and definitely more than is usually therapeutically advised). Those interviews won't be complete until everything has been dragged out of you in graphic detail.
You'll probably be expected to trust on demand a succession of random people. You might build some trust up with one police officer over the course of your interviews and then suddenly without warning they'll be reassigned and you'll be expected to carry on with a stranger.
Once they've put you through the wringer and searched your life history they might - might - consider creating accurate records and they might possibly consider asking your parents some questions. Maybe. If they're elderly or have health problems it is unlikely they'd be arrested for that.
And then because this is non-recent abuse and they'll deny it and blame you it will all be dropped.
If it went to court you would be ripped apart and explicitly blamed and accused of being a fantasist. And then a bunch of people will decide a verdict based on random irrelevant stuff like whether or not you were emotional enough or if they think elderly people should go to prison (seriously, look at people describing the decisions and discussions that happen in juries).
And even if you got a guilty verdict people would insist it was a miscarriage of justice and attack you. Some people would believe and support you, but lots of people refuse to accept guilty verdict when it makes them uncomfortable.
I don't think you'd get through any part of it without ending up with additional trauma (because of our shitty system, not because of you).
Basically, it's shit. And it's wrong. It's horrific what you've lived through and are living through, and it's horrific there's no way to have the truth heard or hold people to account.