1. not sure but would have thought any alt.
2. not sure but would have thought would maintain system pressure to essentials
3. charge air through ducts and cool air around ducts
4. unimportant - only if the generators are paralled on a synchronous bus does the phase have to be the same. If the generators are operating on a synchronous bus and one starts misbehaving, current transformers along the cable runs input signals to Generator control units and bus control units which trip split system breakers, generator circuit breakers or bus tie breakers dependent on situation