What fonts are used in the assets? Can I use them commercially?

The sample font varies by product and may not be included in every marketplace package. For example, The Stone GUI kit uses Changa in its sample design: Changa on Google Fonts. Check the exact product guide and downloaded package instead of assuming one font list applies to every asset.

Before commercial use, download the font from its official source and review the current license, redistribution, embedding, and attribution terms. A font being free to download does not mean every use or redistribution is unrestricted. Replace the sample font when its license or supported characters do not fit your project.