I’m a little fuzzy on how you have things set up. Series and sessions, where a session is always in a single series. And then display a series with all the sessions in that series- or a single session and link back to the session it’s in, all that should be pretty easy with relationships.
And now on the media page (http://www.phoenixfirst.org/media) that bit is working, but the problem is how to show the two most recent session entries- and the two should not be in the same series.
If that’s the case… there isn’t a great way to use categories here. There isn’t a tag for showing categories ordered by the most recent entry in the category, which is what it sounds like you would need.
If I understand everything, I think you might need either a custom add-on or a little creative embed/nesting. So to get the very latest entry in sessions, just use a tag limited to that channel and a limit of 1. That works no problem- yes? IF that works no problem- you could pass the id of the related entry as an embed variable, and then use it in a custom query that figure out the latest session entry that is NOT related to that series. But like I say- it would be a custom query.
I don’t love either of those. I’d be tempted to write an extension that maybe updates a custom field in a channel whenever something is related to that channel. Then I could just use a channel tag- show the series channel, order by that field, and limit to 2.
But short answer- I’m not thinking of a totally out of the box solution. Did the brainstorming give you some ideas, though?