Yes I would say that he is stealing them and smoking them, I wouldn't say anything to him that will let him know that you seen this or that your pills are missing. Try hiding them else where and see if it is still happening.
Yes it sounds like he is doing exactly what you think he is. If only you and your mother live in the house and then when he comes around and pills are missing and foil is in the bathroom, ummmmmmm ding ding ding it is him no doubt. HIDE YOUR MEDICATION. Do not let him get a hold of them even if you have to keep them in your pocket while he is around. Trust me we as addicts will find those pills pretty much. I matter where you hide them, if we know they are in the house WE WILL FIND THEM. so keep them on you when he is there. I pray for the best for your brother, also know that you can not help him in any kind of way until HE wants it for himself. All you can do is be there for him when he finally makes the choice that enough is enough. Be there for him for support only, do not give him money. If he comes around saying he needs money for something then tell him ok well let's goto the store and I will buy it for you. By giving him money that is only enabling him and keeping him in his addiction. He has obviously not hit his rock bottom yet. My prayers are with you and your family. And man oh man I heard that crystal meth is really bad. I know first hand experience how bad pills are, but he is also battening crystal meth. Double prayers for him.
Yes, that sounds highly suspicious. Trust your instincts when it comes to this. Us addicts are fantastic liars and manipulators. Stealing pills from friends/family (or strangers!) is addict behavior 101.
I'm not sure how your mother could press charges for stealing meds w/o your bro being caught in the act. BUT, it's worth a shot...anything to give consequences to the action of your brother. Your brother has obviously not hit bottom yet. I don't know the living arrangements but whatever you do, do not give him ANY cash and do not coddle him in any way. The addict needs to have his own bottom in order to want to change. If you enable him, that won't happen.
I highly suggest you and your mom go to alanon. It is literally a group created because the loved ones of addicts are at their wits end. You will not only get support, you will get fabulous info on how to deal w/ an addict.
Keep checking this site. It's late and more folks will be chiming in later:)