Is it permissible to secretly take money from the family's funds to compensate for what was spent on renovating the kitchen, and would the amount be considered a supererogatory charity if one waives their right to it with the intention of charity?

If the supervisor of the kitchen renovation made financial decisions that led to a shortage of money, there are two scenarios: 1. If he donated from his own money: There is no blame on him, and he is not required to inform the partners. 2. If he borrowed from himself or from others: The permission of the partners is necessary, and he is not allowed to borrow without their permission, because he does not have the right to obligate others to a debt except with their permission. Jurists have permitted borrowing on behalf of others only in cases of necessity, such as the wife's maintenance if her husband refuses, or borrowing on behalf of a partner in a building with the ruler's permission to repair what has collapsed. As for borrowing on behalf of partners without necessity, it falls upon him and his money, and the partners are not obliged to repay the debt unless they consent. Ibn Qudamah said: "He is not allowed to borrow against the company's money. If he does, then that is for him, and he has its profit, and upon him is its loss."

Based on this: If you gave charity with what you did with this money, you will have its reward. And if you inform your mother and siblings, if they agree to repay the debt, then so be it. If they refuse, you cannot compel them. You are permitted to take what you put the money into, if possible without harm, because it was purchased with your money.