OP, I feel your pain. We live your neighborly nightmare every single day. Unfortunately, we are at war with our neighbors. This started one afternoon not long after we'd moved in when someone -- I have no idea who it was -- called the police because Neighbor Guy was blasting his music incredibly loudly. I happened to be in the wrong place at the wrong time, and Neighbor Guy assumed it was me who called the police. I promise -- it wasn't me. In fact, I'd planned to go over and talk to him about the loud music, but I had to pick DS up from school first. Because they assumed erroneously that I called the police, they became obnoxious and unreasonable about their noise. In essence, I never had a chance to talk to them first. Instead, they made a huge, "interesting assumption" about me. Now we have to call the police. And we do.
My advice to you is to go over there and talk to the neighbors about the noise before someone calls the police. This is probably the best first step you could take if you want to avoid a war. If they refuse to keep it down, investigate the noise ordinance in your city. If they appear to be violating the noise ordinance, then call the police and let them deal with it. In some cities, violators may be cited and fined in court. In our city, it is difficult to get the police to issue a citation; however, we have been encouraged by the police to call every single time we suspect a violation. So we are -- in the hope that they'll eventually be cited. In the meantime, we are documenting by recording their noise in case we want to take them to court for interfering with our fair enjoyment of our own property.
Please do talk with your neighbors before taking any other action. "Hi, I know you probably don't realize it, but the noise from your parties is pretty loud. It's disturbing us. Would it be possible to keep the noise down after X time?" See how they respond. If they're obnoxious or unreasonable, you can escalate as needed from there.