As soon as I got the option to escape my family to Obristan I decided that was the ending I wanted to get. And it wasn't too hard either, because I only had myself my wife and my niece to bring.

I know I definitely confiscated 3 Obristan passports (Including Jorji's), which should be enough. And I know I had enough money ($250 at the time I decided to leave). Yet for some reason in the end cutscene it tells me that my niece got left behind in Arstotzka.

Anyone know what happened?

You still need to pay for rent, food and heat. If your wife and niece are OK (not hungry/sick/very sick) and others are dead, then you can uncheck food and heat. 3 Orbistan (red) passports are enough. Escape should cost you $75.

Well, as I said in the above post, I had all of that covered. Thanks anyway though.

Turns out the problem was that the mother-in-law was dead. Apparently her and the niece will only escape with you if you have both of them. Don't have the niece then the mother-in-law won't come. Don't have the mother-in-law and the niece won't come.