Sims characters breading like rats
What you are seeing is normal for MCCC's default settings.
Move in homeless sims: MCCC will override the gameplay setting even if it is unchecked. So if you don't want NPCs moving in, you need to shut it off in the MCCC option. Also the results vary if you have aging on or off for NPCs. If you play with it on, you can fill your houses up with babies that never age up. I play with NPC aging on so they will grow up and die.
In addition to what @RandomBuzziness has said, there are a couple more things you can do.
Under MC Command Center > MC Population > Moving Settings > Open Houses Default is 1. You can raise that number to reduce the number of lots that NPCs can be moved into. I use 2.
Under MC Command Center > MC Population > Moving Settings > Homeless Apartment Percent Default is 100. You can lower that to reduce the number of NPCs that move into the San Myshuno apartments. I don't know if will work for those in Evergreen Harbor. I have mine set at 25.
Under MC Command Center > MC Pregnancy > Offspring > Maximum Household Offspring Default is 3. Lower that to slow NPC family growth. I have mine set at 1. There is also a Maximum Offspring option also with a default of 3. But that one will affect your playable sims too so unless you don't want twins or triplets, leave that one alone. Or if you want your playables to have more multiple births, say quads, then you can raise it to 4. It doesn't affect how often a multiple birth happens, that is still random, It only allows you to decrease or increase the number of babies that can be born at one time. I learned this after lowering it to 1 and then noticed that I wasn't getting any twins anymore. It took me quite a while to figure out it was this that was causing it because I thought that it was only for NPCs, but apparently not. After I changed it back, I got twins and a set of triplets. And I still get twins every now and then.
Under MC Command Center > MC Pregnancy > Marriage Percentage Default varies by age group but YA and Adult is at 20. You can lower that to lower the number of NPC marriages, thus fewer kids in the game and slower overall NPC growth. I have mine set at 10.
One other thing. If you have the Vampires pack, don't make NPCs vampires because they will never grow old and die. Or if you do, delete them or cure them. If they marry and have babies, chances are that a good percentage of them will also be vampires. So you can fill up your game with NPC vampires if you play a save long enough. I did it in a test game to see if it could happen and proved to myself that it will happen. Took awhile I but filled up every house in WC, OS and Newcrest as well as Forgotten Hollow. I do use NPCs to get the create 5 vampires milestone, but I make a note of who got turned and once I get the aspiration completed, I go into Manage Household and delete them as I don't want NPC vampires in my game, just my playables.
Hope this helps.
