Using fonts

Sorry, a rather basic question, but I couldn’t understand it from the docs: if I have a child theme, and I choose some google font (in the font picker), will I loose it when updating Gantry? Should I add it to my yaml file?
And one more: if I wanna use only one font, do I need to set it in both fields of the picker? Won’t it load the font file twice?

Thanks

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