I get this when i try to use fonts

By default path searching is working in CURRENT directory. For example you have folder layout

-Assets
-- Fonts
-- Views

Then in in XAML placed in view folder you use Source="../Fonts/<path>". ../ is one-level up.

FontFamily property uses family names, not font files. So the xaml should look like this: Noesis will take care of matching the family name plus the font properties (Weight, Stretch and Style) to the corresponding font file.
To make sure you use the correct family name you can inspect any Font asset and check the "Family" string that Noesis will match.