So, I observed the mechanics of the Group Instance and discovered some factors, which also leads to my curiosity as follows:

1. The Tailed Beast Jinchuuriki Group Instances' Ninjas always start after all of your teams have attacked, but in Kage Trials, they act the same way as normal pvp would. (They would attack according to initiative value and position compared to you).
Q. So how much initiative value do you need to outspeed them with your ninjas at the same position? Or better, how much are their initiative value? (e.g. 2 Level 5 Refines, etc. or something?)

2. Third Hokage Hiruzen Reaper Mystery activates immediately after he comes back to life.
Q. Is it possible to interrupt his mystery before he uses it?