Complex query (?) problem

Wondering if someone might help me out here with a problem … my apologies if this isn’t making sense, but if someone could help, I can try to better explain myself and problem if I’m not communicating the best here.

I’ve got a site where I have set 2 categories, 1 with multiple sub-categories – we’ll call them 1 and 2 (children of 2 are 3, 4, and 5). On my main page, category 2 is a random entry of it’s children, while category 1 displays below that. When you go to the previous entry of category 1, the page should display the same way – randomly selecting category 2’s children (3, 4, and 5) with category 1 below.

However, category 2’s children are also category pages where I have a comments link and the page still renders out as it does on the main page – which I don’t want to happen. I would like to pass a variable (?) that says, “if this single page is from categories 3, 4, or 5, do not display the parent category (2) above the entry below (which would actually be 3, 4, or 5).

Is there someone that can help a pretty basic noob understand how to make this happen?