Justin Simmons and Will Parks have the speed, athletic ability, and potential. 
But they are not mentally ready.  Time and again, they were out of position and chasing Buffalo's mediocre receivers.  
Sanders has to hold on to the ball.  On his long catch, the ball was moving.  Maybe it was a fumble.  In any case, why put the decision in the refs hands?  Just secure the ball.  That was a big momentum shift in the game.