Optimising Google Fonts

Hi! I’m looking for a good way to optimise how the theme (Multicorp) uses Google Fonts and wanted to see if you could give me a hand. I can see that at the moment the theme is loading two sets:

– My own fonts from Google, defined in the admin panel:
Fira Sans + Fira Mono
– Other fonts:
Lato, Open Sans, Indie Flower and Oswald

The issue is:
I need to make sure the theme only loads the fonts and weights I really need.
I only defined three of them through the admin panel (Fira Sans regular, Fira Sans bold and Fira Mono regular) but it’s loading the full set of weights (300, 300italic, 400, etc).
It’s also loading the full set of the other fonts I mentioned above, making each page needlessly heavy.

Could you give me a hand avoiding this behaviour? :)
Here is a link to the site in case it helps.

Thanks in advance!