What is the ruling on selling his share in a company whose wealth is all debts that are owed by people?

Praise be to Allah.

With regard to the first question: this is selling money that is not available for money (cash) that is available, but of a lesser amount.  This is not permissible. 

With regard to the second question: he should sell him his share of the cars and keep for himself his share of the deferred payments.