I served my ex-brother-in-law's custody papers meant for someone else now he's coming for me directly

I got home from work last Tuesday and there he was, standing in my driveway with a sheaf of papers in his hand. Liam. I hadn't seen him since he walked out on my sister three years ago, leaving Chloe with nothing but a birthday card that arrived six months late. He shoved the papers at me and said, "You've been poisoning my daughter against me. I'm taking this to court." I stood there in my work clothes, clutching a bag of groceries, and watched him drive away in his white ute.

When I actually read the documents that night, I nearly laughed. The application was for my sister's new partner, Ben, not me. There it was in black and white - "the respondent, Benjamin Wong" - but the address was mine. Ben had moved in with my sister three months ago, but he'd used my place as a mailing address while his lease was ending. The court had served the wrong person. I sat there on my couch, a glass of wine in my hand, and I had a choice to make. I could call the court Monday and clear it up, or I could let Liam's own sloppy paperwork sink him.

The preliminary hearing was last Thursday. Magistrate Singh looked over the file, then looked up at Liam with an expression that could cut glass. "Mr O'Shea, your affidavit repeatedly references 'the respondent's new partner' but the respondent before me is a single woman. Can you clarify this discrepancy?" Liam's face went red. He started stammering about a mix-up, about how he'd meant to serve Ben but the address was wrong. The magistrate asked him directly: "Are you aware that you have served your former sister-in-law with a custody application that does not name her?"

That's when Liam doubled down. He amended his application on the spot, now naming me directly. He claimed I had been acting as Chloe's de facto parent, that I had a duty to facilitate contact, and that my text messages proved I was hostile to him. Then I got the notification - he'd screenshotted a private text I'd sent my sister and posted it to the family group chat. The text said, "He doesn't deserve to see her. He abandoned her." In the chat, his parents started piling on, calling me a liar and a troublemaker. My own mother called me crying, asking why I was making things worse.

Magistrate Singh dismissed the whole application. She said Liam had no standing because he had not been a custodial parent for over three years, and the improper service made the whole thing invalid. But then she looked at me and said, "Ms Chen, I understand your protective instincts, but your sister needs to engage with family services. This court cannot order a future placement without a full family assessment." She ordered that before any future applications, my sister and Chloe would need to attend counselling and a parenting assessment. I walked out of that courtroom with a moral victory, but my sister called me later that night, terrified that the court was going to take Chloe away. I told her it wouldn't happen, but I don't know if I believe that myself.

So, AITA for not correcting the paperwork error and letting Liam's case fall apart on its own?