To talk about how many of something there is in Chinese, you need a measure word between the number and the noun. This is kind of like saying One piece of paper or Two cups of coffee. The most common measure word in Chinese is 个 (ge).
三个学生
sān ge xuésheng
three students
她有四个姐姐
Tā yǒu sì ge jiějie.
She has four sisters.
We also need a measure word after 这 (zhè, this), 那 (nà, that) and 哪 (nǎ, which).
那个人
nà ge rén
that person
哪个老师?
Nǎ ge lǎoshī?
Which teacher?
Use 没 (méi, no) before 有 (yǒu, have) instead of 不 (bù, no).
她没有妹妹。
Tā méiyǒu mèimei.
She doesn’t have a younger sister.
我没有你的电话号码。
Wǒ méiyǒu nǐ de diànhuà hàomǎ.
I don’t have your phone number.
In Chinese there are specific words for little brother, older sister, etc.