3 sentences

1. 他是大房的长孙。

   tā shì dà​fáng de zhǎng​sūn.

   He is the eldest grandson of the first branch of the family.

   Source: Dong Chinese Dictionary

2. 作为家中的长孙，他从小就肩负着继承家族事业的重任。

   zuò​wéi jiā​zhōng de zhǎng​sūn, tā cóng​xiǎo jiù jiān​fù zhe jì​chéng jiā​zú shì​yè de zhòng​rèn.

   As the eldest grandson of the family, he has borne the responsibility of inheriting the family business since childhood.

   Source: Dong Chinese Dictionary

3. 长孙无忌是唐朝著名的宰相。

   Zhǎng​sūn Wú​jì shì Táng​cháo zhù​míng de zǎi​xiàng.

   Zhangsun Wuji was a famous chancellor of the Tang Dynasty.

   Source: Dong Chinese Dictionary