Is the husband obligated to financially assist his brother in building a luxurious house to please their parents, knowing that his brother holds a higher degree and works, but aspires to a higher financial standard?

Obeying parents is not an absolute obligation; rather, it has specific conditions. Their obedience is obligatory in matters that benefit them and do not harm the child. Therefore, your husband is not obligated to help his brother with this amount, and his refusal is not considered disobedience. However, if he can help him with this amount or less, as a way of showing filial piety to his parents and earning their pleasure, it might be better, and Allah might open doors of goodness and blessings for him through it.