Missing Twin

Yeah, as above, eating for two just means that the pregnancy test is positive (currently only sure of having at least 1 baby). The game on it's own can't tell you if there are twins, but using the MC Command Center does allow you to find out gender, number of babies, and change those things. I'm not sure if the "simfirstname" was maybe just a minor glitch? If there was another sim family you had been playing that was expecting, there's a chance the game glitched and gave you a notification from a different family. Other than that, I'm not really sure what it could've been.