Thanks for your opinion, well the first 1, (A & B), would be with FA on-board.
1. In flight, I was thinking first I would assume that cockpit door should be closed and locked at all times, I would assume this would be in the SOP's. So would be FA's to deal with this whole issue, with possible diversion required and contacting the police/security to meet after landing if that is required.
Am I correct it would also be possible to ask for assistance to restrain the person while on-board, until we arrive destination, however this would be the FA's duty to arrange, however I would assume that they would keep the pilots informed of the situation and the seriousness.
(However could this be a trick question, in that they expect you to know that the cockpit door should be closed, and you should not get involved?)
On the ground, I would assume again would be FA's job to sort out, in the case of not being satisfactory explained and calmed down, call security and have the person escorted of the aircraft.
2. The Smoke, of course with limited knowledge/experience, of course I would ask the Captain why, as I wish to learn. So more questions about this, but it is knowing when to questions something that might be plausible but at the same time, might not be, and might be an issue that needs to be resolved.
I guess educating yourself best possible, is the only way to be able to know how accurate the explanation is or might be.
3. Is very tricky one indeed.