My first question regarding such an operation is;
Why are you making the first of such flights at an airshow/ large gathering of people?
Not saying that it could be but to an independent observer, "showing off" would be high on the list of posibilities and that is something you must ensure that it is not.
Ask yourself why aircraft fly in formation and what the advantages/disadvantages of such an operation are especially with dissimilar types involved.
Unless you have practiced the procedures well then a busy airfield (airshow or not) is the last place you what to try it out.
If on the other hand, you and your friends are in the habit (practice) of operating as a formation (perfectly legal) then provided that you were simply arriving at the aerodrome in the way you normally do (formation break into the circuit perhaps) then IMHO no display authorisation is required.
Have plenty of practice before hand somewhere quiet and it will work out better on the day.
Remember that the formation break is only one method of arrival, it is not unusual for a formation to stream while some distance out and perform a standard join one after the other.
Regards,
DFC