Am I entitled to object to my husband lending his brother money to build his house, and to the brother selling a portion of his land to my husband in exchange for the debt, knowing that my husband believes I only have rights over my own money, while I believe I have the right to intervene in how he disposes of his money?

The husband should involve his wife in shared matters and consult her, with the wife understanding that consultation is not binding. As for helping the brother, the basic principle is for a person to start with himself and those he supports. However, the brother might see that it is better to deter his [other] brother from engaging in usurious borrowing, while noting that a loan which brings a benefit by selling a share of the land is not permissible.