I actually held two discussions about Families in Worldbuilding, but this was during Google+'s technical hiccup and only one of them got recorded to Youtube. Oh, well!
I spoke with Glenda Pfeiffer, Jaleh Dragich, and Misha Gericke, and before we met I made a list of some types of families I could think of. It's a long list.
Four-person nuclear family
Family with special needs children
Child living with grandparents
Family with two mothers
Family with two fathers
Family with two mothers and two fathers
Family with adopted children
Family with divorced parents
Family with divorced parents and step-parents
Suffice it to say that there are lots of different kinds of families, and some of these types can even combine with other types. Families are complex, and they can also change. I suddenly became an aunt six times over when I married into my husband's family, but it took us several years before he became an uncle in mine. It's a good idea to think through how many options there are so you don't fall into using default settings. And in fiction, very often those default settings involve families that have been changed by death. I've even seen the theme of creating your own family from friends you care about (more than once). If you actually work with a family that is alive (like, for example, Sunday Woodcutter's family in Enchanted by Alethea Kontis), you get a much more complex and interesting situation. There are also some inherent problems in using dead people as motivators. Too often you get "women in refrigerators" who serve solely as motivators for men and their pain ("manpain"). Misha said that very often when she sees revenge movies involving the death of a family member before the action of the story starts, she doesn't really care about the main character or why he is doing what he's doing. I mentioned the movie The Funeral (Juzo Itami), a comedy, in which the disagreeable father of adult children dies in the first scene, and the entire action of the film features the children and other relatives having to deal with each other and feign love for the dead man during his funeral. That was a fascinating family story, especially since the adult children were actors by trade, it gave us a chance to despise the man before his death, and then watch its consequences for the family members.
Misha mentioned, rightly, that it is sometimes difficult to align family with the plot that you intend, so this may be the reason why people often strip families away. However, it can be good to have a supportive family against an external enemy - and while it's natural for families to come together against enemies, they are also a great source of tension and conflict, even when they are not totally dysfunctional!
Glenda and I specifically discussed the question of dead parents, and while she and I both agree that the loss of parents can serve effectively as an inciting event, this needs to be handled carefully. We shouldn't diminish the impact of grief on the child who has lost parents, and sometimes it seems that children are being treated as people with no attachments, rather than as people who have experienced a great loss. I asked what the implications of the loss of a parent were. The answer to that question depends on the setting. Does the society allow for orphans to go off and seek their fortunes? At what age? Is it reasonable for a 14 year old to be making it on his/her own?
In my Varin world, there are a lot of rules, and not a lot of places for kids to land if they leave their homes. One of my characters loses her father and gets kicked out of her family because her mother can't make enough money on her own to support her. This means that it's next to impossible for my character to earn any money, and she actually steals the identity of a dead friend and sneaks into their family so she can get back into a part of the social system that will support her and allow her to go on to an adult job.
Glenda spoke about her own work where there's a clan system with strict rules. A teenage girl who is a member of a clan split off from a larger community, suffers a disaster along with them and becomes the only survivor of their clan. She's then taken in by the larger community but is treated like a poor relation. Saladin Ahmed creates a situation much like this in Throne of the Crescent Moon, because Zamia comes from a clan that has split off from a larger community and then subsequently gets massacred.
This brought up the question of "Once you're an outcast, how do you get back in?" It's a good one to pursue in stories, and often the answer we see in movies is "Create your own family from those whom you trust." It would be interesting to see other possible answers.
Our next question was, "Do families have to be dsyfunctional?" It's a trickier question than you might think because of the bias toward conflict in fiction. Is it true, though, that wholesome families are boring? I don't actually think so. Every family relationship creates a situation where someone is unable to leave the relationship behind without enormous difficulty, and simultaneously creates a need for negotiation. Every family member can have individual quirks and there's plenty of tension available there without having to have the whole place full of psychopaths or falling apart at the seams.
Aliette de Bodard uses families in an interesting way in her work - I'm thinking specifically of her Nebula-nominated story "On a Red Station, Drifting." She bases the societies on China and Vietnam and actually has memory implants that preserve the voices of a person's ancestors - their family - so that they continue to guide that person. Quite a fascinating twist.
In fact, there are tons of family parameters that can differ. Do the adults interact with the children? In some cultures, children learn to speak from their many older siblings. In others, the eldest children provide child care for the parents. In still others, it's rare to find more than two children per family. Child discipline is handled in a lot of different ways even within a single culture. Many of these conditions are heavily influenced by surrounding societal factors, so make sure to think through those when you are creating your families, to understand whether they are usual or unusual, and in what way, relative to the society you're working with.
Fiction tends to create a drive for simplicity. It makes sense, but it doesn't take that much work - or even that many words, to add an additional layer of contrast and interest.
Families have their own ways of working through issues like disasters, threats, social pressures, even something as small as talking about a new book (Glenda told us about the difference between her reception, and her cousins' family's, to Harry Potter). But cohesion takes work. Families are constantly enacting their relationships, and enforcing them. How often have you heard a parent say, "We don't do that. We do this." Think through what kind of enforcement of family roles, and of personal behavior, will occur in your family context. People are constantly recreating and enacting the social contract, even in work situations. There's a lot of careful social grease that goes into making families work.
This makes for wonderful story opportunities.