Posts (by category) show on certain pages

I am very new at website related stuff, but agreed to take on the (as it turns out) very large project of developing a site for a volleyball club. The problem I’m having right now is, I need to restrict certain posts to show, via the “recent posts” widget, on certain pages. For example, I want any post related to the “15s” team, to only show on the “15s page” this is for security reasons, as eventually I hope to restrict access to those who are registered as affiliated with these teams (a whole other forum, I’m sure). I am using the “Widget Logic” plugin, which is doing a great job of putting the widgets where I need them, and I have simply created a different “recent posts” widget for each separate page, however when I us the category tag: in_category(4) is does not redirect the posts, they still show on every page with the “recent posts” widget.

In my reading, I’ve come across this “loop-page” thing, but that doesn’t seem “friendly” for as many pages as I need to do this for (approximately 10?). Any help is greatly appreciated!