My Parents Lied To Me

I went to my sister Charelle's house today for the first time in nearly 2 months. I talked to Naomi (the one who called the police) and she said she wasn't very clear about the reasons why she left when she first told me. I knew part of this story because I'd went to see my brother a few days earlier and my Mum used her petty "I've seen/experienced worse" tacticon Naomi, She said she was self harming while she was living with us, and had attempted suicide 3 times, all because of my Dad who she said ignored all her attempts to have adult conversations with him. At 12 she said "Dad, I know you miss your family back in Nigeria, so if you ever want to talk about it, I'm here." Everytime she said she'd had a shitty day at school (she used to be bullied) my Dad would, in a nutshell, say "grow up" or "I've seen worse" or "It's a test of character" instead of actually trying to solve the damn problem. When Naomi told Mum she had been self harming, she said "Look at my scars, Naomi", and that is when Naomi stopped the conversation. My Dad said if Naomi wanted to leave he wouldn't have stopped her, but earlier in the day Naomi said that he said if she did try to leave, he would stop her. And the entire reason she called the police was so she could be escorted out safely, especially Charelle's baby. For some reason, I believe Naomi. She said she has nothing to hide and had no qualms about disclosing her shortcomings, something my parents make excuses for or do not mention at all. I didn't suspect my parents of lying, so I just went with what they said. Another thing they said was that Mum stays neutral until something is said about her, and Naomi explained how she is a lonely person who is afraid of Dad leaving, so will nod her head with everything she says. I knew my parents could be biased a lot of the time, but I never thought they'd outright lie. What should I do the next time they disclose information about something?