If you look at the research 4% of incest reports are lies. So that makes 96% who are telling the truth.
I don't know the evidence based research on other disclosures of other types of abuse. Someone else might have two cents to put in.
Some people will believe that a young person has made "false allegations" even when the father has served time in jail for the sexual abuse of his daughter, so you need to be very careful of going down the false allegations track. My father used it to get access to a lot of children. And my siblings said nothing happened to them to be able to be alive and exist in their predicament. That has changed as time went on and they were far away from my father.
I respect your current position. But I respectfully disagree. There is something really wrong there when a young person tries to kill themselves, acts out, is suicidal, uses drugs and runs away from home. Those are not the actions of a young person who is in a safe, secure place with loving and attentive parent/s.
Your daughter did not deny the allegations when you challenged and confronted her. I do wonder why is that so?
J took a knife to school and was suspended for threatening another child if I remember correctly. This, too, is not the action of a child in a safe home.
Where are your granddaughters getting their behaviours from? What are they mirroring?
Your daughter has prioritised her relationships and being in domestically violent relationships over caring for her daughters - there is profound neglect in that equation at the very least.
I think more will be revealed as time goes on, but that is only my humble opinion though.
And intergenerational trauma is really tricky, you are three generations and you all have a lot going on for you.
I think you have been hammered lately especially with the latest news outside of this, so self care and self compassion may be a way to go.