Is it permissible to take the amount from the father of the debtor whom I guaranteed, knowing that the father is a merchant, and if the father refuses to pay, what is the solution, and is it permissible to take the money without his knowledge?

If the sponsored person (makfūl) is in hardship, then it is obligatory to grant him respite, as Allah Almighty says: "And if there is one in hardship, then [let there be] a respite until [a time of] ease. But if you remit [it] as charity, it is better for you, if you only knew." If you doubt his truthfulness, you may sue him to ascertain his hardship. As for recourse to his father and compelling him to pay the debt, there is no basis for it unless the father had guaranteed the payment of the debt, and it is not permissible to transgress against his property.