He does not sell by selling his brother's.

Muḥammad b. ʿAbdullāh al-Raqāshī > Yazīd b. Zurayʿ > Muḥammad > Ibn Isḥaq > Yazīd b. Abū Ḥabīb > ʿAbd al-Raḥman b. Shimāsah > ʿUqbah b. ʿĀmir

"I heard the Messenger of Allah ﷺ say, 'It is not permissible for a believer in Allah and the Last Day to sell a transaction that has already been sold by his brother until he leaves it.'" – Sound Chain

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الرَّقَاشِيُّ حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ حَدَّثَنَا مُحَمَّدٌ هُوَ ابْنُ إِسْحَقَ عَنْ يَزِيدَ بْنِ أَبِي حَبِيبٍ عَنْ عَبْدِ الرَّحْمَنِ بْنِ شِمَاسَةَ عَنْ عُقْبَةَ بْنِ عَامِرٍ قَالَ

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ «لَا يَحِلُّ لِامْرِئٍ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الْآخِرِ أَنْ يَبِيعَ عَلَى بَيْعِ أَخِيهِ حَتَّى يَتْرُكَهُ» – إسناده صحيح