After sending a second email with the full history of the recent matter, in order to inform my landlord of any misinformation they may have received, I received the following short reply:
[My landlord] will have them park on the street. He will talk to them and have them abide by his rules. From here on out if you have a problem with them call [my landlord]. [phone number redacted]
Wow... I can't say I'm surprised to see the issue resolved in my favor (though I imagined it could have gone the other way as well) but I do wonder what exactly caused such a quick and complete reversal. I figure it must have been either the knowledge of the previous hit-and-run (I can't imagine a landlord being happy to hear that their tenant's guests are committing crimes), or perhaps they did indeed feed my landlord a bunch of lies about the situation and my landlord isn't at all happy about it.
Regardless of the exact reason, hopefully that solves the problem. My stress level was becoming rather high over the issue and so I'll be quite happy to go back to not worrying about what the hell is going on outside.