Talking about family members in Chinese is very complicated due to the Confucian emphasis on relationships and hierarchy. (See also Mates, Terms of Endearment, and Addressing Strangers).
For example, the English word “cousin” has 8 different Chinese translations depending on mother’s side or father’s side, older or younger, boy or girl. By the way, don’t be fooled when your Chinese friends appear to defy the One Child Policy and tell you about their 5 brothers and sisters. They frequently leave of the cousin-indicating prefix and just call their cousins “older brother” or “younger sister.”
To simplify the task of wading through the myriad of family terms, I’ve made a visual representation of the relationships and terms, which is available for download below (click on the picture).

Chinese Family Tree.pdf
(requires Adobe Reader, which is available here).
NOTE: To download the document directly to your computer without viewing it in your internet browser, right-click on the link and select “Save link/target as…”
You’ll notice it doesn’t include the great grandparents’ generation. This is because many Chinese don’t know the technical terms for great grandparents, such as “zēngzǔfù 曾祖父” (”great grandfather on father’s side”), and it would be easier just to say, “Grandfather’s father” in Chinese to get your meaning across.
In addition to the terms and tips on the Chinese Family Tree.pdf, here is some vocabulary I’ve found useful when talking about family members and relationships.
General Family Terms
qīnqi 亲戚 = relative
zǔzōng祖宗 / zǔxiān祖先 = ancestor
qīn gēge 亲哥哥 = real older brother (same parents)
qīn jiějie 亲姐姐 = real older sister(same parents)
xiōngdì 兄弟 = brothers
jiěmèi 姐妹 = sisters
xiōngdì jiěmèi 兄弟姐妹 = siblings
fùmǔ父母 = parents
zhàngfu hé qīzi 丈夫和妻子 = husband and wife
àiren爱人/ pèi’ǒu 配偶= spouse / lover
nǚpéngyou女朋友 = girlfriend
nánpéngyou男朋友 = boyfriend
yīng’ér婴儿 = infant / baby
xiǎoháir小孩儿 / háizi孩子 = child
Oh, by the way, I’ve left out the arsenal of in-law terms. If you’ve got a reason to learn those, well, you’re on your own.