With Cloud Layer V2, the way light is propagated from one cloud layer to another is through the GI cache. The "light propagation" parameters don't transmit light between cloud layers, only within the same layer. Therefore Cloud Layer V2 usually doesn't handle this kind of scene as well as Cloud Layer V3 can, but it might be possible to tweak your GI settings and/or the colour of your lower clouds to make them look more integrated. I would start by looking at the following settings. GI quality at least 4. Cloud colour in each layer: 0.25. In the upper layer, reduce the light propagation setting and try to get the upper layer to look good with the lower setting (perhaps by reducing the density to compensate for the lower amount of light propagation). This will reduce the difference between the amount of light reaching the upper and lower clouds, and perhaps if the upper layer has a low enough density you will get some sunlight reaching the lower layer. Finally, raise the colour of the lower layer slightly to compensate for it being darker.
These changes might get you closer to a realistic result. But if you can use layers of Cloud Layer V3 instead, you'll probably get better results and more detail in the lighting of the lower cloud. You might only need the lower cloud to be V3 to get this benefit, depending on how closely they overlap, but it's probably safer to change both of them.
Matt