Plans and Dreams
Despite their various plans and intense hatred of Yosef, the brothers may never have been able to gather the 'courage' to actually kill their sibling. Had they heard him screaming, they may even have retracted their plan to sell him. Nevertheless, they talked, they planned, they plotted, and therefore they are considered guilty even though they never did actually kill Yosef or sell them.
Nonetheless, the Hand of Providence led them to believe that their 'dream' [to rid themselves of Yosef] had come true, while in reality, it was the fulfillment of Yosef's dream that was beginning to unfold.