In regard to the Visa question… I can't speak for anyone else apart from BA, but at BA, as a rule, we only have one passport, be it flight or cabin crew.
We only have one requirement for a Visa, which is the good old US of A. So, when we attend out Visa appointment at the US Embassy, they take our passport off us that day, and it is
usually returned to the concerned person within 3-5 working days. Over that period, no flying can, obviously take place.
When it comes to passport renewal, BA have an agreement with the Passport Agency in the UK so that they will issue us a new passport without us having to send in our current passport which is approaching expiry.
So, as we don't have a requirement for more than one Visa, we have it quite easy in terms of documentation. If someone personally choses to use more than one passport, be it of differing nationality of length of validity, then the passport which has the Visa held in it must be used for entry to the USA on work trips.
If that passport expires before the end validity date of the Visa, then the expired passport is retained and presented with the new valid passport for entry.
In regard to the rest of your questions… In an ideal world, we would evacuate our area, and assist where possible. Of course, our first aim is to empty the aircraft in under 90 seconds. We use commands to ensure we draw evacuees to exits that are not being used or away from ones which are being over-used etc. where possible. We also do the opposite and "guard and re-direct" when appropriate to not use "our" exit. All, of course, is dependant on conditions within the cabin. There is a elemental degree of "looking after ourselves" in regard to our own life, and if conditions become a threat to our lives, then we will leave the aircraft before any remaining passengers, who may unfortunately be unable to make it out before a change in cabin conditions. There are several well documented cases of cabin crew sacrificing their own life to assist others, and not making it out.
This fine lady was one of the earlier ladies to do so:
Barbara Jane Harrison
More on the incident:
BOAC Flight 712
All of what is said is in an ideal, classroom/mock-up based situation, however, who knows how any of us will react when faced with the real thing.