| | Re: How many people do you have in your family?
Excellent post that made me double-check my own usage. I use and hear both on a regular basis, but I also work with so many non-native speakers that one can begin to doubt your own language instinct. Mesmark certainly has an excellent point about the implied power dynamics in some situations (work, etc), but I'm not sure it's a universal principle here. Like many common expressions, a detailed logical analysis will reveal patterns that may not be intended by the speaker or perceived by the listener.
For what it is worth, you inspired me to check what I wrote in my new conversation textbook (Compelling Conversations) in a chapter titled "Describing Family Ties." Shock, shock.
"1. Do you have a large, medium, or small family? How many people are in your family?" The combination seems likely to provide both perspective and precision.