Yes, you can sell debts on and this is done all the time between companies. Many companies sell their debts or invoices to factors and the factor will chase the debt and collect payment.
Alternatively, you may find they instruct a debt collector.
I'm not surprised that they're not interested in the third director, they know where you two are and so will chase you for payment.
However, if this man has threatened your husband then I would definitely inform the police.