Current flow through diode
If it was 0.7 V across the Si diode, then it would be 0.7 V across the Ge diode, since they are in parallel. How much current do you think would have to flow through the Ge diode to achieve that voltage?

Here's a diagram:



(http://www.rfwireless-world.com/images/junction-diode-characteristics.jpg)

If we extrapolate around a voltage drop of 0.7 V for the Ge then I believe the \$I_F\$ for the Ge diode will be around 200 mA. 

Is there 200 mA flowing through your Ge diode with 3 kΩ resistance?

No

So the voltage drop across the Ge diode will be around 0.3 V, what is the current for the Si diode at a voltage drop of 0.3 V?

Close to 0 ampere ≃ open circuit

So if you want both to conduct simultaneously, then you would decrease the 3 kΩ resistance until the point in the diagram above when both have current flowing. 



I do recommend you to watch some youtube tutorials. Especially videos by Dave Jones. His videos were like a second teacher to me during my time at the university. And I also recommend using CircuitJS, my third teacher. Simulate, simulate, SIMULATE.