I do believe it is not rule breaking simply because A kills B. B switches to Hessian. C later switches to the Corsair. Both switch their characters and since
"A player who was killed in a PvP fight must not attack the enemy (character or characters involved in the death)"
B was killed, he switches to Sair, his sair is not connected/involved with the death of his other character so it's free to engage. Atleast that's what I think. Correct me if I am wrong.