Millers chairman Denis Coleman admitted his side had no choice but to sell the pair.
"Williamson wouldn't sign a contract, while Hoskins was offered a deal and refsed to sign it," he told BBC Radio Sheffield.
Coleman also hit out at the conduct of Hoskins' agent Imre Varadi.
"Will asked that I talk to him through his agent, but that is ridiculous," he baslted. "He doesn't need advice on the matter of whether he wants to stay or go, and he should have told me one way or the other."