I changed the existing family with the one where they have a toddler (from the gallery by Maxis) & do nothing.
ETA:- Not that I don't know what to do with them, but, I would prefer to have a natural story progression among them. So far, I'm too busy with my own Sims & can't be bothered with the premades. Perhaps, if one day, we're going to have personality, chemistry or anything related to be patched, I might considered to get them to divorce if they do not have a good chemistry or let them to work it out, if they're meant to be together. I won't split a family that I don't know very well. :wink: