This is how to put the single - common legend when you have made a single plot with multiple axes.

single_legend_multiple_plots.py

handles_0, labels_0 = axes[0].get_legend_handles_labels()
handles_1, labels_1 = axes[1].get_legend_handles_labels()

handels = handles_0 + handles_1
labels = labels_0 + labels_1
fig.legend(handels, labels, loc=(0.83, 0.85))

"""Here, the main function is `.get_legend_handles_labels()` 
it will return the labels and handles for individual plots

Then we have to make a GLOBAL list that covers all handles and labels
and then finally put them in the legend call"""

From this question: https://stackoverflow.com/questions/9834452/how-do-i-make-a-single-legend-for-many-subplots-with-matplotlib