I have found a work-around for the "Twin Glitch", You play your pregnant Sim right up until her 3rd trimester (when you hover over the baby moodlet there will be a ????) from there you switch households for about two days and when you come back, she would have given birth!
You might miss the birth, but to me that is okay! I haven't tested it up till she goes into labor, so if anyone wants to switch when she goes into labor, feel free to test it out and report back!
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EDIT:
I moved my sim out right after she went into labor, and she did NOT have twins!!! I tried this twice and she had one baby each time, they were both girls.
Sims 4 Comic Legacy