I had planned to mention that I have awesome mod, but then I forgot. I don't have either of those though. I only have the base game, but the most recent patch (aside from one for some of my store content, apparently). This doesn't seem to be a rental situation because it doesn't give me any options as a landlord. I did a save as, but haven't gone to check my previous save to see if they were there then. I don't remember exactly when I saved last, but I was doing a bunch of renovating on the new place so I was saving often. It's likely that they were already there.
I've had sims own multiple homes before and this is a first, though granted I haven't been playing long this time around. (I used to play when the game was new but preferred TS2 and switched back. Giving 3 a second chance.)
*edited to add*
I checked my last saved game and they were already there then, so I can't get back to a time before they moved in. I switched households and there are a bunch of other glitchy things going on with the Loboses. Marisol is pregnant, but she doesn't seem to know it. Her baby bump is obvious and she's in maternity clothes, people can interact with her belly, but she has no pregnancy moodlet, she can't get checked out at the hospital, she's not getting any pregnancy related wishes, and she's still going to work.
She's stuck at 0 days to aging up to elder because of the pregnancy, but life fruit doesn't give her more time nor does it affect Angel's age (87, 88, 89 days old so far). This is odd. I'm glad these glitches aren't happening to my main game family.