How to make each subdomain look the same as the home page (site.pl)? All links in the menu and links on the home page in subdomains are intended to link to the main page (site.pl).
Can it be done so that each subdomain in multisite automatically updates to all changes on the main page?
There is no way to do it as is. Each subdomain (each website) is independent, with own database tables, settings, active theme/plugins.
You would need to add some custom code that will be triggered when the main domain front changes (you also need to figure out how to detect the change, is it in the theme, or menu items or content), and then replicate changes to all subdomains. Again, this can be tricky if your changes are in content, settings and/or theme.