OOB - Both Players Have Possession?

[CDurham]

Player A1 is holding the ball. Player B1 approaches and touches the ball and his back foot contacts the sideline.
-OOB on B1, Team A will get a throw-in??

The ball is loose and player A1 and player B1 dive for the ball, when both grab ahold (before a jump ball can be called) they both contact the sideline; or just player A1 contacts the sideline.
-First situation) Go to the arrow?
-Second) OOB on A1, Team B gets a throw-in?

Thanks!