Why does the sister know Russian?
That's not convincing. In The Bureau the brother and sister of course knew Arabic. Edit: I know I wasn't particularly clear here, but I don't find it convincing that her brother has been some sort of deep agent for the KGB, has told her, and on her own she's gone off and learned Russian presumably to join him at some point when a CIA agent happens to show up that she can drag along with her? That plot line makes sense in the original because you have a sister who wants to join her brother in the Islamic State, but by introducing the KGB angle you've complicated things unnecessarily by making Viking a bigger deal than he was in the original. And that's reflected in the unbelievability of the sister knowing Russian and somehow being a KGB adjacent accomplice.