For using a single transistor to turn a LED on when a current gets over a set level see here;
Motor over-current sensor
and you don't need R3 so its 3 resistors a trimpot and a transistor.
You can start with 2 of those circuits, one will light the green LED if the fan is drawing normal current, the other circuit lights the red LED if it draws too much current.
Another transistor can turn off the green LED if the red LED is lit, so the fault condition gets priority.
That covers all your needs, if the power fails (or fan is open circuit) no LEDs will be lit. If running ok the green LED will be lit. If overcurrent fault (stall etc) the red LED will be lit.