Well, you don't really have a say in who they have as guests. They're allowed to use their property as a revolving-door halfway house if that's what they want (unless they're involved in people-smuggling, which will be hard for you to determine).

However, if they're imposing on you through noise or casual trespassing, you do have a recourse for that.

Re: The trespassing: One possible course of action would be to try and reason with them regarding the number of people stepping on your property. Say something like

"I know this sound nitpicky, but that's a LOT of people walking across my lawn every day. Is there anything you can do to have your guests not walk on my lawn anymore?"

And then put a camera up, covering the problem area including the run-up to your neighbor's house. Put it in an obvious spot and make sure they know it's there. Now they know you know they're using their place as some kind of immigration halfway house (because you refereed to them having 'guests'), AND they know you have a picture of everyone's face who comes and goes.

And when it comes to the noise, complain to them a lot and give them ample warning so that it doesn't come as a surprise when you finally resort to calling the police.

This way you're recording everyone who's coming and going, and you've got the police's attention on them. So if there's anything fishy going on there (like maybe people smuggling, if not just health and safety concerns), they'll shut the fuck the up and stop bothering you, just to avoid any trouble.