Problem with take-off in formation
 

I created a couple of missions with six bombers taking off in scramble. When I test them with the AI in control, everything works fine: the aircrafts take off by pairs and join formation after a while, following all the assigned waypoints. But when I play, the others follow me only after a time and they fly round and round if I wait for them at height or if I go my way to the target. Is there any option or command to have them in my tail at take-off?

Not in my experience.
This is a symptom of one of the most annoying bugs in CoD- you need to use autopilot for a bit at the start of a mission to 'register' players plane with the game.

If you are flying as a wingman this isn't too bad, a quick on/off of autopilot is sufficient and you can takeoff normally and fly the rest of the mission.

If you are Sqn/flight leader I find it necessary to keep autopilot on until ~1st waypoint otherwise your wingmen will 'ignore' you for the rest of the flight.

That's my experience anyway

I tried and you are right. No problems if you fly as a wingman. Well, in some sense to be a wingman is not so bad. In Blenheim and Br.20 you don't have to care for the course :)

Yes, I confirm that this bug happen if you lead the squad. Anyway this seems to happen if you don't follow exactly the mission path just after take-off. It is not (only) related to autopilot. If you fly following the path, commonly the AI don't retreat.