With firewalld, you can also configure it like I did in this post and it will do everything correctly also
Since all your computers are behind the mini pc they are NAT’ed from the internet which means unless routing is enabled as per @Xino’s post or by configuring firewalld to NAT the packets, then they won’t be able to get to the internet.
The link inserted doesn’t format well, but when you visit the post you’ll see it correctly formatted and the steps required to configure firewalld.