"Yes, B will always go before C or D. He will also never go before A, assuming prompt jutsu on both sides."

As i felt in game, if "B" have much more developed refinement or/and has a faster jutsu, he can cast his mystery before "A". As example - Guy/Iruka. Sometimes they interrupt my Main on turn 2/Hinata on turn 1 and sometimes - no. Guy has really slow jutsu, in 7 cases out of 10 he uses interruption too late(especially in rankeds). But Neji/Crymson Fist interrupt opponent's jutsu in 8-9 cases out of 10. Magic.