If Eldest Brother says that disagreeing with the marriage is harming him, then so be it, agree to the marriage. Then it's not harming him anymore, is it? He says I don't care for him, fine, after the marriage, the bride can learn the rules under my watch and earn her keep! He accuses me of favoring my younger siblings, alright then! I'll treat all my sons equally and act as if I never raised such ingrates; I'll just pour my affection onto my daughter.
After all, most of the sons were almost raised by their grandmother and have limited affection for me.
They say I treat my sons like long-term laborers, that I want them to earn money, to drain their blood to support my natal family and my daughter. Well then, I brought them into this world, having them earn money to support me in old age and repay the debt of life is only fair!
Since the mother-son relationship has come to this, I no longer care.