Family - Idiomatic Expressions

Here are some idioms to talk about your relatives:

We're as different as chalk and cheese.
We're like two peas in a pod.
We get on like a house on fire.
She's the spitting image of her mother.
I have little to do with her.
You just can't tell them apart.

And do you know...  

What's the difference between stepsister and half-sister?
What's a godfather? And a great-uncle?
What's the difference between immediate and extended family?