@IsoujiX
That's cause he really love his family and he include his twin in that family circle. Since he IS the eldest brother, in these type of chinese situation, the elder brother usually kept and give all the good stuff to the younger sibling. In this case, the little brother who's he's been estrange for 20+ years for was very happy with a single elemental sword, he figure he would gift him with more happiness with two more sword.
Its familial love and obligation. Too bad the second brother had it made but he just toss his relationship away. Of course he might still forgive him but we'll see.