Random townies decide to live in my house?

@theFrostySlime You could try a couple more things.

• First you will need to make sure they are all out of the house so you don't lock them in.
• Update your game to the latest version.
• Untick the 'Fill Empty Homes' setting in "Options Menu > Game Options > Gameplay" in the game save.
  Move your household out. If the other family is still there, evict them. Exit the game and save, then come back and move back in.
  Then immediately:
• Add the 'Private Dwelling' lot trait:
  
• Make sure your front door is designated:
  
• Lock ALL doors & gates to "Everyone But Household Members":
  
• Now on the front door select from the 'No Trespassing...' list/menu choose to disallow anyone you wish:
  

@theFrostySlime Sulani has always acted a little different in my game too. Are your random townie invaders food stall vendors? I get those plus other random townies from that festival area next to the Tangled Flat lot who show up at my Sim's house (Tangled Flat) and even if I lock them out they will just stand outside the door all night and into the next day. There is no bathroom out there for them to use so usually they will just chat or play with their phones until they get too tired, hungry, or are on the verge of a bathroom emergency. If you use MCCC there is a cheat command in MC Cheats called "Make Sim Leave" that usually works for me.

I fixed it (people coming into my university dorm) by travelling with all the randos and not coming back with them. I also locked my doors 🙂 istg I'll kill them if they return

edit: they returned so now I'm cheating building my dorm so that the hallway is blocked off from the rest of the dorm

edit 2: turns out I didn't need to do that. I just sent one of them home, omg! My problem came from adding a stove to the dorm and having an incomplete lot or smth, bc apparently university students aren't allowed to cook (apart from using micorwaves and fridges)....

I've had this happen with Santa (no really). I recommend what @infinite101_  suggested: Travel with them (preferably to a park during a blizzard) and then immediately go back home without them and lock all doors.