Did some fool from a Chinese forum told you to post that here? Probably. For starter, you are not investigating a crime. But since you and whoever told you to post that nonsense have never served, you do not know how military people work and think. Simple as that.
People talk. In joint exercises, people talk. From maintainers to pilots to group leaders -- people talk. And they talk about everything they see.
Regarding item one -- stupid. The most you can do is establish their bona fides, meaning their IDs, and that is all. You have a bunch of pilots so of course their
TECHNICAL backgrounds will be %90 similar if not %100 identical. So trying to interrogate them as if they are suspected of a crime would get laughs and if any walk there is not a damn thing you can do about that. They are not Chinese citizens that you can intimidate. Lastly, when they talked to you, the British embassy would know where they would be.
Regarding item two -- also stupid. There is a difference between technical and tactical and here is the difference...Teaching you how to take off and land is technical. Pull the yoke this way, kick the rudder that way, and move the flaps so and so. How to take off and land in a crosswind is tactical. The crosswind create variable flight conditions and that would necessitate slightly different flight controls actions in the cockpit.
Regarding item three -- also stupid. Sure, you can propose some test questions to experiment if each of them know what they are talking about, and sure, all of them would agree to that reasonable argument. But once your questions breach into the tactical realm, they would shut up. Why should they continue? What they know are valuable and as the Joker said to the gang leaders: "If you're good at something never do it for free." You are the one offering me money for what I know of air combat tactics, and now you are trying to get that knowledge for free just for 'testing'? Sorry, pal, but you came to me, remember? Either pay me my contract or am walking, and my embassy know where I am.
Once you paid me my contract price, what can you do to me? I can train your pilots outdated air combat tactics and there is not a damn thing you can do about it. For starter, your pilots have no combat experience in the first place, so how would they know BS from facts? You think I cannot cook up BS? You are at a disadvantage here. In a joint exercise, everyone observe everyone else. But you came to me, remember? I am retired. I came alone and in your playhouse. I notice everything while there is nothing for you to take note. People talk.