A long while ago, when I was handling SP for the first time, I turned off the ability of sims to move in together. The reason was that they kept on moving from the houses I build specially for them, the setting I changed made them stop moving. I used those settings for years, modifying and exporting/importing them into new towns.
Now I actually want the sims who are newly wed to move in together, but I cant figure out what I must change to make it so.
I hope you guys can help me out.

There is no SP caste or selection filter for Newlyweds or Just Married. Not sure this is going to work, but it's worth a try...

NRaas > SP > Town Options > Household: Allow Move As Family > False
NRaas > SP > Town Options > Household: Allow Move Solo> False (unless you wish to allow splits/solo moves otherwise)

Create a new caste (called whatever you like), set Automatic to True, Caste Filter to Stranded Couples > True
NRaas > SP > Caste Options > (your new caste) > set both move options to True

The Caste Options should trump the Town Options for sims who are members of the caste.

I will try that, but it will probably take a while to see if it works as I have engagement set to like 30 days.