Is close-aircraft formation at supersonic speeds possible?

I'm curious and would like to know if it is safe (any adverse effects?) for two aircraft flying side-by-side (about 10 to 20 meters apart) to maintain that formation while:

1. Accelerating from the same subsonic speed to the same supersonic speed?

2. Accelerating from slightly different subsonic speeds to the same or nearly the same supersonic speed but with slightly different accelerations?

3. If a third aircraft were to join them from the side, from behind, above or under, would it be adversely affected by the "shockwave cones" of any of the two aircraft already at supersonic cruise?

I'm curious about how the air around them would behave when the "shockwave cones" of each aircraft touch each other...would they cancel each other out or do something else (get amplified or diverge it converge).