https://www.youtube.com/watch?v=nDrH0173sIc
This is Carl's Guide, and I used this to help figure things out.
I did forget one tiny detail. Be careful with how quickly you build the relationship. I managed to stack so many powerful happy moodlets onto Calum and Arihi that they both almost died from hysteria before they had kids. Actually, I did have to start over a couple times because Arihi laughed to death before getting to the bed and Calum swam around playfully until he went belly up in the ocean. I admit, I was still figuring out the game.