the coulpe were living together before they get marry might the reason that we can't add a baby in sims.
I have tried to let two new sims to be a partner each other.
then the sim of woman promise to the man, this is the first time for me that the couple both show 'engaged' at the same time
then I bring them to the woman's house, and let the woman ask him to move in.
after that, let them being romantic until there are full of pink color of ''engaged'.
I let the man get marry to the woman, I am so happy that I can add a baby after that
but....I still have two couple can't show 'married' at the same time.....so sad....
I think it is because they have lived together so fast...
I tried to divorce a couple, but one still show 'married' after that...even if one is get marry with another...now, three of them are living in the same house:(