How manyth son to your father? [duplicate]

Solution 1:

I don't think you can ask that question directly. The conversation could go something like the following:

How many children does your father have? To which the answer could be three.

You could go on and say:

Which one are you? To which the answer could be I am the youngest, oldest, second, third, etc.

Now the last question might seem ambiguous if it's standing all by its own. But it would make sense once it's in context.