Spaceships questions

[SCAR]

Some questions on Spaceships, I have an idea of some of the answers, but I'm not entirely sure so some confirmation would be helpful!

1. Crew and Crew Shifts - Clarification
The calculation of suggested crew requirements is fine; but then some of the ships in later volumes state that they carry multiple crew shifts.
Does this mean multiplying the crew requirements by 2 or 3 for multiple shifts?
The answer must be no, since that would increase Life Support requirements, and most of the designs seem to have the right number of cabins (etc) for the basic crew requirements.
I therefore assume that the reference to 'multiple crew shifts' simply means that not all of the crew is likely to be 'on duty' at the same time (under non-emergency/'red-alert' conditions).
Is this reasonable?

2. Combined deltaV - Clarification
The notes on the External Clamp system discuss how to recalculate/combine acceleration, but I can't find anything stating how to calculate the result of combined deltaV.
I'm assuming the calculation is basically the same as for acceleration:
Multiple the total deltaV reserve by the Mass for each individual 'spaceship'
Add these figures together for the combined vessels.
Calculate the total Mass of the combined vessels (along with other masses being moved).
Divide the first total by the second to get the combined deltaV reserve for the combined vessel.
Is this correct?

3. Spaceships Engines in an Atmosphere - Questions
(a) Which of the Spaceship Engines cannot be used in a 'standard' (habitable) atmosphere?
(b) Which of the Spaceship Engines would be hazardous to use near a population centre? - This might be on a sliding scale: Rock Landing Area well away from populations; Spaceport outside of town (this assumes the landing pads/bays aren't slagged by engine exhaust); Can land on the edge of the average town, say in a car park or equivalent; Could land in town square; Could land on top of a building (say the equivalent of a heli-pad).

Space Sail obviously don't work in an atmosphere, and I'm not sure that Electric Engines would (not sure why I think that though)? How about the Plasma engines from SS7?

Engines with 'Nuclear' reaction mass would be 'unsafe', Nuclear Salt Water would seem to be pretty hazardous, and the EPP (Orion Drive) is definitely not for use anywhere near a habitation!