Your closest relatives are your parents: your mother and father; and your siblings (brothers or sisters). If your mother or father is not an only child, you also have aunts and / or uncles. An aunt is the sister of your mother or father, while an uncle is the brother of your mother or father. Your female child is called your daughter, and your male child is your son.
If your aunts or uncles have children, they are your first cousins. (In English, the word cousin is used, whether the cousin is female or male.) Your female cousin is your mother (or father's) niece, while a male cousin is the nephew of your mother and father.
When you marry, your husband (or wife's) family become your in-laws. The mother of your spouse (husband or wife) is your mother-in-law and his or her father becomes your father-in-law. The term in-law is also used to describe your relationship with the spouses of your siblings. So the husband of your sister becomes your brother-in-law, while the sister of your husband becomes your sister-in-law. If you are a woman, you become the daughter-in-law of your husband's parents, and if you are a man, you become the son-in-law of your wife's parents. The same term in-law is used for all generations. The husband of your aunt is still your mother's brother-in-law, for example.
Grandparents / grandchildren
The parents of your parents are your grandparents – grandmother and grandfather. You are their grandchildren – either a granddaughter or a grandson. If your grandparent has a sister, she is your great-aunt. If your grandparent has a brother, he is your great-uncle. (And you are either his or her great-niece or great-nephew.)
The mother of your grandmother or grandfather is your great-grandmother. The father is your great-grandfather. If you go back another generation, the grandmother of your grandmother / grandfather is your great-great-grandmother. The grandfather of your grandparent becomes your great-great-grandfather.
If your mother or father remarries, you can acquire a new family and set of relatives. For example, if your father marries a second wife, she becomes your step-mother. Any children she already has become your step-sisters or step-brothers.
If your mother or father remarries and has children, they become your half-brothers or half-sisters.
You might also hear people talking about their biological brother / sister etc, to mean a brother who is related by blood, rather than by marriage.
Types of family
nuclear family = mother, father and children: "The traditional British family unit is a nuclear family."
single-parent / one-parent family = a family which only has one parent (because the parents are divorced, or because one of the parents has died): "There are more and more single-parent families in the UK."
immediate family = your closest relatives: "Only immediate family members attended the funeral."
extended family = your entire family: "The wedding invitations were sent to the entire extended family."
close-knit family = a family where the members have close relationships with each other: "They are a close-knit family."
dysfunctional family = a family where the members have serious problems with each other: "He comes from a rather dysfunctional family."
blood relative = a relative connected to you by "blood" rather than through marriage: "She's not a blood relative, but we're still very close."
Expressions with family
family gathering = a meeting / celebration of family members: "There's a small family gathering next week."
family resemblance = where members of the family look / act similar: "You can see a distinct family resemblance between the father and the son."
to start a family = to start having children: "They want to wait a couple of years before starting a family."
to run in the family = a characteristic that is common among family members: "Baldness runs in his family."
to bring up / raise a family = to have and look after children: "It's difficult to raise a family on one income."
a family car = a car big enough to transport a family: "The Volvo Estate is a popular family car."
family-size = large quantity item: "We need to buy family-size packets of biscuits!"
family-friendly = a policy that favours families: "This hotel is family-friendly."
family doctor = a doctor who looks after general medical needs: "There are a number of good family doctors in this area."
family man = a man who prefers to spend his time with his family: "John is a family man."
family values = traditional ideas about what a family should be: "Some political parties often emphasise family values and the importance of marriage."
family name = surname: "What's your family name?"
Describing family relationships
Children often quarrel with each other, and these arguments – or squabbles – are often quickly resolved. In fact, sibling rivalry (the competition between brothers and sisters) is quite common.
More seriously, if arguments continue into adulthood, family feuds can develop where both sides can end up hating each other and even trying to hurt or destroy each other.
A person who no longer speaks to a family member is estranged from his / her family. Often estrangement is voluntary. However, if parents decide they no longer want anything to do with their children, they cut them off (= break off communiation), or even disinherit them. (Decide not to leave them anything when they die.)
Most people feel loyalty to their family, and will defend family members saying "He / She's family". There's also a saying "Blood's thicker than water" which means that your family ties are stronger than any other relationships.