"How DO native speakers ask.....?" The notion of 'birth order' is far less significant in Western cultures than it is many other cultures. As Chris says, it would be an unusual question to ask. When siblings are young, it's usually obvious what order they were born in; in adults, it rarely matters. With the exception of royalty, Western families do not generally observe a system of seniority among adult siblings : there is no reason to treat or refer to a third brother any differently from a second brother, for example. If you happen to be curious about someone's family, you might ask something like this: 'Are you the oldest..?' or 'Are you the youngest'? If you meet someone's brother or sister, you might ask a question such as 'Is he/she older or younger than you?' or "Who's older? You or him?". Or if you know that someone has several siblings, you might ask a question like, "Who's the oldest?". The other person might then offer the information e.g. "I'm the oldest. Next comes Anna and then Sarah", or "I'm the middle one. Anna's two years older than me and Sarah's two years younger". The commonest number of children in Western families is two, so the question rarely arises - a simple 'older/younger' query is enough. It's fairly unusual for families to have more than three or four children, so there's usually no need to enquire in depth about order. In unusually large families, you might say something like "Really? You're one of eight? Wow, that's a lot. So where do you come in the family?'. At this point, they might say "I'm the third: I've got two older sisters, one younger sister and four younger brothers."

US - we don't ask. It is not a question that comes up. Occasionally, if someone is already talking about their brother or sister, we might ask "are they older or younger?" But we wouldn't go into details and not unless there was already a discussion about the family.

I normally say, "How many children are in your family, and who is the oldest and youngest?"

(Hope you're asking about birth order of siblings) "In what order where you and your family born?" Or "Who's the youngest to the oldest member of your family?"

Thank you