Questions on Shared Internet Connection

Hi dear,
I have 1 MB connection and it is shared between 4 peoples. Also I don’t have modem. I have only cable connection. Modem is in my friend house.
1 Tell me some method so that I can check who is online.
2 Can I disconnect some other person internet because some time I do downloading due to use of other person’s internet. My Downloading speed becomes very slow.
3 Also tell me can I access other person computer without his permission.
Regards
