I'm going to utilise the spoiler tags as I fear this is starting to creep into spoiling it for everyone.
First of all, I'm aware of three characters and I believe there are meant to be 5. A little girl, the elderly lady and the man.
Secondly, the leg grab is indeed the staff just running up and down the train grabbing hold of you. I assume they'll know the exact timings or will have something to indicate to them which section the VR is playing.
thanks. Just watched that BBC news video that I posted earlier in this topic, and it looks like there's an older man, younger man, young boy, young girl, and older woman. Don't know if the infected people are different. Think I had a teenage girl as the infected person.