I have had my sims game with mods for a few months (mod knowledge for years) but for some reason on this save file, the townies are literally getting married and having babies in one day. I even slowed down the relationship-building steps from SP, but it didn't do anything. Is there a way to make relationship building, and moving onto the next step (dating, engaging, married, kids) go slower? I am trying to do a slow burn and play my game with the intent to have generations come through.

When you say you slowed the relationship-building steps in SP, what settings did you change? What overall SP setting are you using, and have you changed the speed of any of the managers further than that?

You can also increase the "cooldown" between certain steps, e.g. Cooldown: Marriage to Pregnancy, which is the number of days between the marriage and an expected pregnancy. That doesn't cover unexpected pregnancies, and you should be able to tell the difference if you're seeing SP notifications: the text makes it very clear whether the sims were trying to have a baby or not. You can search the documentation page for cooldown to see your options:

StoryProgression-Interactions

Finally, is this a new save file, and are there any high relationships or pregnancies between unmarried sims when the town first loads? If so, SP might be marrying off parents-to-be or those with very high relationships already, sort of as an initial push to reorganize relationship status to reflect the other details.

Hello, I wish I could provide that information to you, but I had to do a total reset on my game due to a glitch beyond my understanding. However, I am back online and ready to start a multi-generation/reincarnation storyline that I wish to play for a while. I would very much like to have several seasons go by in between next stages like from dating to engage, married to having a kid.
my dilemma before was that everyone was having a baby (5-6 over night) and no one was aging up, and lots of people losing jobs because of the babies. I want to avoid over population by having a healthy number of townies.

MsRaccoon post_id=98032 time=1701576427 user_id=24301 wrote:
my dilemma before was that everyone was having a baby (5-6 over night) and no one was aging up, and lots of people losing jobs because of the babies. I want to avoid over population by having a healthy number of townies.

In Storyprogression you can set

Pregnancy: Base Number of Children
The base number of children the sim wants to have. This value is adjusted by trait-scoring.
Default: 3
change to 1

and this
Pregnancy: Maximum Number of Children
Determines the maximum number of planned children a sim can have. This does not stop unexpected pregnancies from occurring.A setting of "0" means unlimitedNote that multiple birth pregnancies can exceed the value specified here.Default: 0
change to 2. or even use 1 too

If you need more babies or f.i. you want a couple to have another boy or girl you can use
Mastercontroller
1. MasterController-Interactions#Partner-Pollinate

2. then specify the gender MasterController-Interactions#Baby-Gender

Or even use Instant baby, specify gender to have it immediately.

This way you can regulate and plan your population grow.

​​​​​​Under MC Demographic - Population you get a stat how balanced your population is.