All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon Prophet Mohammad and upon all his family and companions.
The owners of the company are obligated to pay the Zakah due on their company`s money once it reaches Nisab (Minimum amount liable for Zakah) and a full lunar year elapses over possessing that amount. The amount of Zakah, due on the company`s money, is calculated and each partner is required to give the portion due on his share or they may deputies one of them to give the due Zakah.
However, it is permissible to pay Zakah to one`s son who is in debt provided that three conditions are met:
First: The debt has fallen due as it isn`t permissible to give Zakah to a debtor whose debt is deferred.
Second: The debtor doesn`t have the needed money to pay off the debt since if he is able to pay it off then it isn`t permissible to give him Zakah.
Third: The debt wasn`t incurred in an act contrary to Islamic Law.
Commenting on giving Zakah to debtor, An-Nawawi (May Allah have mercy on him) said: "If he had borrowed money to achieve a benefit of his, then he may be given from Zakah to settle his debt, but with conditions. One of them is that he is unable to pay it off. However, if he could pay off some of it then it is permissible to give him only the amount that he needs." {`E`anat At-Talibeen, V.2:317}.
In conclusion, it is permissible to give the Zakah due on the company`s money, with the assent of the partners, to the son who is in debt provided that the debt has fallen due, he didn`t have the money to pay it off and he hadn`t borrowed the money for any un-Islamic or wrong purpose. And Allah the Almighty knows best.