Many members on some of the other forms here have mentioned getting a medical lock box or even a little safe , if you can't find a good hiding place for the main Rx bottles.

Hide or lock away the pill containers and only keep what you need for a day on your person or close easy to access in a hiding place.

Sounds like brother needs some intervention /counseling of some sort, but you must keep your meds safe from theft of any kind.

I don't know if confront is the best word , but a calm talk & explaining how missing meds will hurt you physically with withdrawals, and possibly cause problems with refills if it happens often.

If he is at suicide risk, he may be stock piling the meds and not for use as day to day high...

You may have to mention possible legal action if he denies or gets angry.
Sometimes it is the call that does help to get a loved one the help they need.
may need an family intervention...of some sort and request/demand he goes to counseling.
our Survivors of Suicide forum would be a place to find more help on that subject.
http://neurotalk.psychcentral.com/forum29.html
We also have some Mental Health forums at the bottom of the main page, that might be helpful for your brother.
http://neurotalk.psychcentral.com/index.php