Hiya Marco, first off let me echo what Ghosth said. I think you are doing an interesting thing.

A couple of options I can see right away to help you out with others interfering in the TA.
Have you considered assigning a vox channel to your team?
For those without Vox capability you can just type the number into any of the other radio channels, and what they type will only display to those tuned to that number.
Or (and not sure if you have done this yet or not), you can set up a Squadron in the TA and tune everyone to squad on one of the text channels.
And lastly...The field at A1 is probably not the ideal place to hold meetings or train. Everyone is deposited there as soon as they log into the arena, hence it becomes a pretty busy field.
I would suggest moving to a field farther away from the action to practice.
It is unfortunate, but you will likely get very little cooperation from those around A1. They are there to engage in fights and practice ACM for the most part (and indeed it is one of the purposes of the TA).
If the AH Demo Team is what I think it is, good luck with it.

And I look forward to being a spectator at your first show.
<
> Young Fella,
cheers,
RTR