How is it supposed to look when you need to gather people who are army, air force, and navy in a group (as in a joint force). I’m talking a smallish group less then 60 people.

Would they be 3 separate formations? Would they all fall in together? Would one branch be together in a squad/element etc?

Is there actual guidance in a document somewhere? I keep finding only branch specific guidance but not for mixed. I’m dealing with a mix that is about percentage wise 85/10/5 of people in different branches.