(1) Perfectly safe.
(2) They mean the set/reset pulses applied to the base must not take the base voltage lower than minus 6V (i.e. 6V below the emitter voltage, which is at 0V), to prevent breakdown of the base-emitter junction.
As your file is in some weird format I can't open it, but as long as your supply is only 6V, you should be OK - increasing it to 9V (without taking precautions) will blow the transistors (reverse Vbe breakdown).
The Vbe spec means the emitter may NOT be more than that higher than the base - or it dies.
(1) Perfectly safe.
(2) They mean the set/reset pulses applied to the base must not take the base voltage lower than minus 6V (i.e. 6V below the emitter voltage, which is at 0V), to prevent breakdown of the base-emitter junction.
So lets see if i fully understand. If i make the base more than 6v lower than the emitter the transistor will die. But if i make the voltage on the base 6 or more volt higher than the emitter the transistor will stay alive?
No, it will die. If the base-emitter junction is forward-biased via a current-limiting resistor (i.e. 6V is applied to the base via R3 or R4 in your bistable circuit) the base voltage will automatically be about 0.6V. If you directly connect 6V (not current-limited) to the base the junction will burn out.
The bistable multivibrater circuit has no coupling capacitors so the base never goes to a negative voltage. The set and reset signals float for no action or are grounded to be active.