Chen Hao comes across a family photograph at Xiaoyu's. They compare their families, one large and one not.
Chen Hao
这是你家的照片吗？
Zhè shì nǐ jiā de zhàopiàn ma ?
Is this a photograph of your family?
Xiaoyu
对，去年春节的。我家有五口人。
Duì, qùnián chūnjié de. Wǒ jiā yǒu wǔ kǒu rén.
It is, from last Chinese New Year. There are five of us at home.
Chen Hao
五口人？都有谁？
Wǔ kǒu rén ? Dōu yǒu shéi ?
Five? Who are they all?
Xiaoyu
爸爸、妈妈、哥哥、我和妹妹。
Bàba, māma, gēge, wǒ hé mèimei.
My father, my mother, my elder brother, me and my younger sister.
Chen Hao
你哥哥做什么工作？
Nǐ gēge zuò shénme gōngzuò ?
What does your elder brother do?
Xiaoyu
他是医生，在南京工作。
Tā shì yīshēng, zài nánjīng gōngzuò.
He is a doctor, he works in Nanjing.
Chen Hao
你妹妹多大？
Nǐ mèimei duōdà ?
How old is your younger sister?
Xiaoyu
十五岁，还在上中学。
Shíwǔ suì, hái zài shàng zhōngxué.
Fifteen, she is still at secondary school.
Chen Hao
我家人少，就我和爸爸妈妈，每个星期天一起吃饭。
Wǒ jiā rén shǎo, jiù wǒ hé bàba māma, měi gè xīngqītiān yīqǐ chīfàn.
There are not many of us, just my parents and me, and we eat together every Sunday.
Xiaoyu
每个星期天都一起，真好。
Měi gè xīngqītiān dōu yīqǐ, zhēn hǎo.
Together every Sunday, that is good.
你家有几口人 is the question, and 五口人 the answer. 口 means "mouth" and counts the people of one household, the ones you feed. Elsewhere people are counted in 个, or in 位 when you wish to show respect. Answering 五个人 to this question is understood, but it sounds like a head count of strangers.
Chinese has no word for "brother" on its own. 哥哥 is the elder brother, 弟弟 the younger brother, 姐姐 the elder sister, 妹妹 the younger sister. Relative age is inside the word, not in an adjective, so you have to know it before you speak. The same logic governs uncles, aunts and cousins, where Chinese has some thirty terms.
Three ways of asking someone's age, and they are not interchangeable. 你多大 is for a teenager or an adult. 你几岁 is said to a small child, because 几 expects a small number. 您多大年纪 is for an elderly person, with the polite 您.
