List relevant team members on portfolio item

Hi, I’m developing a theme for a friend’s business. It’s going pretty well, as I’ve done most of it before.

I can’t work out if (and how) to list a team member (custom post type) on a portfolio item. I only want to list the team members that actually worked on the specific case. I’d like it if my friend could just choose one (or more) in the portfolio item admin page.

How would I go about doing something like this? Usually I would Google it but I’m not getting any useful hits with the terms WordPress list post inside post as it seems like a super specific use case.

The page I need help with: [log in to see the link]