Different voltage solar panels in parallel
Putting the two dissimilar panes in parallel is not a good idea.  Mostly, the higher voltage panel will deliver most of the current and the low voltage panel does little.

If the two panels have similar current ratings but different voltage rating, you can put them in series to get the sum of the voltages at the single current rating.  Then use a switching power supply to buck the higher voltage down to what you want.  For maximum voltages under 30 V, it's actually not hard to make your own buck converter.  There are many off the shelf chips that you only need to add a inductor, diode, and a few other parts too.  You can even make your own with a microcontroller if you want to learn more about buck converters.