My BIL keeps telling my nephew to get over his sexual assault

My nephew was molested a couple years ago by a family friend He was 12 at the time, he's almost 15 now. Ever since he doesn't really like being alone with people he doesn't know very well. He doesn't like using the bathroom alone. He has has a few bed time accidents. I didn't even know he had them until he started spending the night at my house more. My sister doesn't believe in therapy. She says it's a scam and her husband has told him he needs to get over it and it happened a long time ago. I don't feel like you can just get over something like that. I was molested and I couldn't just get over it. I had to go to therapy. My nephew used to be a very talkative friendly person. Now he's more reserved and doesn't talk to many people or go out much. My sister didn't want to take the situation to court because there was still family that chose to still be this person's friend and she didn't want them to be mad at her for taking him to court so she decided not to file charges. My nephew has said he doesn't like taking the trash out at night because it makes him scared and nervous and his dad just says he's a pussy and needs to get over it. He doesn't need to get over it. He needs to heal. Honestly sometime I wish I could just have him live with me because as much as I love my sister, she's done a terrible job supporting him through his trauma.