1) 被：我的钱包被偷走了。
 ok 2）被：他的房间被小偷抢了。 no 抢---》抢劫，for “小偷”，you shouldn‘t use 抢，instead “偷”----also，you can use"光临"（have come）in a humor way. 
3）临：临锻炼身体前，别吃饭。-------better say "锻炼身体之前不要吃饭" 
4）临：临去逛街时，请你父母给你钱。--------’逛街之前，别忘了 问/和 你父母要钱“ 
5）临：临做饭前，去卫生间洗手。-----做饭之前要先洗手 For the character "临"，when it means “when （before doing sth）” ，actually it's an old use (in classical Chinese), and nowadays we only use it in very few frequency., for example,"临出门别忘记锁门" 。 for other sentences， we only feel it strange but we can know what that means. Try avoid using it in this way. :D

1) 被：我的钱包被偷走了。
--Correct 2）被：他的房间被小偷抢了。--Correct 
3）临：锻炼身体前，别吃饭。--remove "临" 
4）临：临去逛街时，请你父母给你钱。--临去逛街前，请让你父母给你钱 
5）临：做饭前，去卫生间洗手。--remove "临" ------------------------------------------------------------------ summary: the meaning of "临": ①arrive, be about to, copy, face, just before ②draw, near,approach, descend example phrase of "临" 光临（arrive），面临(face)，临近(approach&near)，临摹(draw)，居高临下(decend)

1) 被：我的钱包被偷走了.
correct. 2）被：他的房间被小偷抢了. correct, 他的房间被小偷"盗"了 sounds better. 
3）临：临锻炼身体前，别吃饭. I could understand you want to use ‘临"to translate "before",isn't it. But its sounds a little strange. Chinese usually say 锻炼身体前，别吃饭. don't need to add 临. Same to another sentences. If you want to use word"临".you could say 临走之前,带上你的书包. which means bring your bag when you are going to leave.