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I agree with your header, but then when I start to read your post you just sound like an asshole.
So let me get this straight, you agreed to invite this person to your party and then got mad when you actually had to be a host to them?
It sounds like the correct thing to do in the situation is to not invite this person in the first place, like what the fuck lol.
This person did not invite themselves anywhere, you quite literally admit to inviting them like???
They asked for an invitation and it was given. They were told to come. If you did not want them there you should not have invited them. >

To be clear, they asked my partner. I was not involved in the asking process. This was supposed to be small, low key, because I still have a lot of work responsibilities. If they were just going to be at the party, cool, no problem. But they're at my house. Multiple days. They're staying here. That's a little more than a one-off. >

Sounds like you are mad at your partner for doing this without discussing it with you first. But those visitors did absolutely nothing wrong.