Hi Purplemaze,
It depends on how the question is presented. If *you* asked the question about your brother, then yes, you correctly chose the 3rd house for him.
If *he* asked the question, and you wrote down the time/place/etc., then he is given to the 1st house.
For legal queries, it also depends on the question. If it involves a judge or courtroom or 'the law' as an abstract, then it's the 9th house.
If it involves the *application of the law* and/or a judgment, then it is the 10th house. The 9th rules the lawmakers, the 10th the enforcers, if you see what I mean.
Also, if you had the impulse to turn the chart (e.g. for 'his 9th house or his 10th house), don't. Use the radical chart, and the radical 9th or 10th. Law is law, not 'his law' or 'your law'. If you didn't have this impulse, well done!
Hope this helps,
Best,
AG