StuStuieHave you tried lowering the max number of sims allowed in your save under game play options? This won't stop townies from appearing altogether, since you'll want to keep some room for the sims you want to add, but it should stop the game from adding so many of them.
Maybe figure out how many sims of your own you want to add in the near future and set that number plus the current number of sims as the max. Then you can increase the max later on when you want to add more.
Right now I have the max set to 80 which is the lowest possible but I noticed it only counts the 80 as active households or favourite households. Often when I make Sims I unfavourite them so they don't take up part of the "80" space.
Thank you so much for replying <3 I appreciate it.
