Okay, it has to be the models.
I'm not dumb guys, I've been modding GTA series (including V) for many years. Pretty confident I was also the first one in the modding scene to discover how to add cars instead of replacing. Unless there's someone who figured it out and didn't release a tutorial.
That being said, these models must not work because I put them all in patchday9ng and it's still not working. They're still default and as you can see it messes up some things such as making the brake lights green colored.
These are the models I used: