Okay so, one of my male Sims who is now a member of the Partihaus club got a little flirty with Eva Cappriciosa during a gathering. A few days later, she called him to inform him that their twin girls "Rosemary" and "Kalia" had been born and were doing great. Awesome news!

But, opening up my game today, I decided to play the Partihaus household to meet the new twins, but to my surprise there were 4 babies there: another two girls named "Lindsey" and "Kaitlyn".
Are quadruplets possible in the Sims? Did another household member have some babies through story progression?
Nope,
All four babies have Eva's last name.
I checked the family trees of all household members, and two of the babies don't seem to belong to anyone. And even more weirdly, the two babies that Eva originally called to tell my Sim about (Rosemary and Kalia) were in fact not her daughters at all. They are not on her family tree, they do not come up as "Daughter" when you mouse-over them, and she cannot breastfeed them, they are just two completely random babies that have somehow found their way into the household!
It will be interesting to see when they age up, if the two extra babies look anything like the other two babies or not.

Anyone else have this four-baby glitch happen to them? Now I've got to decide what to do with the extra two babies, I feel inclined to keep them but four babies is a lot! And it's going to bother me that two of them aren't being recognised as her daughters. I will keep playing and see how it goes. Anyone got any ideas as to how this happened? Is it common?

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EDIT: Screw it, however this may have happened, I have decided to keep all of the babies, after ageing them up in CAS to see how they looked as adults, they are all very much Eva's genetics! And I just remembered it was simple enough to edit their relationship in CAS so make the game recognise them as her daughters. Problem solved!!