I tried that, but it was selecting all ships, not just the one in the same container. Thank you for confirming what I thought it was supposed to do, though. Maybe I'll set that up again and see if I can find something else in the code that is causing the problem.
Would it make a difference that all the gun turrets are in a family and all the ships are in a family? So it actually has the gun turret family has a target, then the ship family bullet speed is set to ...
Indeed, families and containers do not work well together, and it is a known issue that will not be fixed:
In that case, you would have to do the correct picking yourself, I am not able to currently use C2 at the moment, so all I can do is suggesting either to do the conditions for each type of gun turret (easy but troublesome), or to store the UID of the ship inside a family variable of the gun when they are created together, and vice versa so you can add the condition "Ship: pick by unique id, the variable that contains it from the gun"