Double or Single Violation?

[Dennis Nicely]

Yesterday, during a youth game, the following occurred during a one-and-one free throw situation. I was lead and gave ball to the thrower A-1. On the attempt, player B-1 committed lane violation and I blew my whistle when attempt was over. At approximately the same time, my partner blew his whistle because the throw missed the rim entirely. We huddled and decided we had a double violation and used the possession arrow to give the ball to Team B on a spot throw in. Right or wrong?