How to manage bears for Brewmaster?
What I really do for Brew and most micro heroes is set control groups (1,2,3,4) 1 is for the all spirits, 2-4 are for each spirit. As the fire spirit has no active spell, I usually set him to 4.
If you want to learn more about setting control groups for different heroes and micro-managing in dota 2 you can check this guide http://kyubashi.com/how-to-micro-manage/