But once you invoke the police, emergency services and/or the landlord, your neighbor is going to try to involve you as a way of getting back at you for your interference.

It's interesting that you and fourgates are the only people who have brought up the possibility of retaliation against us. It was all I could think about, the time I called the cops. The easy, spiteful, hard-to-defend-against choice would be to call Child Protective Services on us.