Is the wife wrong in opposing her husband, who is helping his brother and his family with money that she has a greater right to for building their home? And does his action please Allah, or does she have a greater right to this money, or should he save it or give it in charity?

A husband's care for his family and his kindness towards them indicate his piety, generosity, and good character. Maintaining kinship ties is among the most emphasized acts of obedience, and giving charity to relatives is both charity and an act of maintaining kinship. A husband is not to be blamed for honoring his family as long as he does not fall short in his obligatory spending, and this is not considered injustice. Giving money to relatives, whether poor or rich, carries a great reward. You should not object to his actions; rather, gently guide him to buy what you need. Do not worry about your husband spending on his family; instead, encourage him to do so, for Allah replaces what is spent in His obedience and expands sustenance because of it.