Visibility of Teemo's mushrooms

Hi,

I recently played as Teemo and against an enemy Teemo. I noticed that I could see their mushrooms as well as my own. So here are a couple of kindred questions I would like help with please:

1. Does Teemo see enemy mushrooms whilst (by default) other players do not
2. Do your own team see your allied mushrooms - so they know where to run to etc. for help
3. I could shoot his mushrooms to destroy them. I notice some enemy players have shot mine in the past. Is this an option when you can see them (for example when you have an item that lets them become visible to you)

Thanks for the help. I'm pretty much Teemo exclusive at the moment so I have no experience playing against the character with another one of my own.