Multiple Categories under one URL, where ‘Front Page’ is used already

In my opinion you should create a new page-child.php and new categories just for that. And assign that page to the blog posts and the new GrupOf categories in use.

Not sure if there is any better solution at least this one will not compromise the rest of the site.

But wait a bit more for some replies maybe someone has a clear / different opinion.

Good luck!

tech