Thank you for your quick response!
I’ve been testing a bit. Now Ajax search pro does show all subsites on the backend, but it doesn’t search in all of them. It only searches on the same 2 sites as before. (And obviously I get search results from only those 2 sites)
Also, I’ve tried using the code that you provided to solve that thing with categories and taxonomies, but it doesn’t work. It throws a 500 error code when I try to search anything on the search bar.
Thank you again for your help, hope we can solve this.