How did Xenia kill the man in bed? The film showed that she choked him to dead by squeezed him between her thighs. Can that even kill a person? In BJJ, there is this kind of move to trap an opponent between the thighs, however, I have never seen anyone say that it can kill a human. I, myself, have learned it as well. I'm no expert, but I don't think it is possible to kill like that. Can anyone explain?
It's a Bond film, so her scissorhold suddenly becomes lethal; it is possible to make someone pass out with that hold in real life, so Goldeneye takes it up to eleven; that Xenia is also not following any rules that might come with a real life fight helps too, but otherwise it's meant to be unrealistic. Sexy, but unrealistic, just like the scene where she does the same to Bond.
A leg scissor hold can most certainly kill if applied in the right place and by a person who's strong enough. If the thigh lock is applied to the throat as a chokehold (a headscissor) most reasonably fit women can knock a guy out with that hold. I don't know that Famke Janssen would have had the power to choke a man to death that way, but a muscular MMA athlete like Ronda Rousey should certainly be able to do so.
As to whether a bodyscissor such as Famke Janssen uses in the movie could kill, it's hard to say. I do know a guy who many years ago had a girlfriend who worked out, and while she was straddling him in bed one day she accidentally squeezed too hard with her legs and fractured one of his ribs. So if the woman works out enough and has the build for it, I'd say it's possible for her to lay a man up in hospital with broken ribs and possible internal injuries at least, if not kill him outright. Again, Janssen doesn't appear to have that much muscle tone, but this guy's girlfriend was definitely more sturdily built.
The novel fleshes it out more and specifies that the Admiral (somehow) has a history of womanising. That makes him an easy target to steal his pass and get access to the ship where the Tiger is on display.
Bond villains are almost always depicted as near superhuman (Jaws, Oddjob, Zoren) In this case Xenia was depicted as being strong enough to crush the life out of someone.