I didn't watch the anime. But from what I read, the room they were in was a big hall. Kircheis was the closest one to Reinhard. The others were quite far away. Minus one or two seconds of freezing moments, and the reaction time to that cannon, no one could have reach or help Kircheis before too late. Beside, Kircheis was shot about three or two times through some of his main blood vessels. He was as good as dead.