As far as fire training, this is part of annual training for pilots which involves occasional extinguisher discharge under Fire Service supervision. Pilots are well briefed on Emergency equipment and locations and all aspects of handling airborne fires.
Most small and modern airliners can be flown by two pilots. But some of them complain that it is not enough, and that a flight engineer makes a real difference in handling in-flight emergencies.
It is legitimate to fly an airliner by one pilot - briefly. The main legitimate excuse for this is a toilet break. The pilot left in the cockpit is supposed to wear an oxygen mask while alone.
Another legitimate excuse is "controlled rest", with one pilot sleeping in the cockpit seat and the other awake and alert.
A passenger airliner with passengers and flight attendants on board has the attendants in cabin. In case of a cabin fire, the attendants are trained to fight the fire in cabin while the pilots can fly the plane and use whatever cockpit controls are still functioning to deal with the matter.
Are the pilots instructed to stay in cockpit at all emergencies (and return there if an emergency happens during a toilet break), or are they trained and allowed to go to the cabin to fight the fire while the other pilot reads checklists and deals with all the technical failures alone?
Again, when pilots fly with passengers and flight attendants, the flight attendants normally cook/warm meals for the pilots as well, and bring them to cockpit.
If the pilots fly just two of them and without attendant, is a pilot prepared to go back to galley to cook a meal, stay away from cockpit till it is completed (and possibly deal with the galley breaking down) and return, while the other pilot is flying the plane alone?
Also, pilots should try and avoid both pilots falling asleep simultaneously. But if it actually does happen, a cabin attendant can open the cockpit door and if neither pilot is awake to override the door opening, the attendant awakens the pilots. If there are just two pilots aboard, this is not an option.