Photos syncing with other devices issue

I have a question about iCloud Photo Stream option. I have a few Apple devices, some of them are owned by other family members, some of them are mine. So if I turned on Photo Stream on my iPhone will it push all of my photos to all of my other devices? I'm not sure if it will, because I don't want it to push all my recent photos to other devices owned by other family members.

Basically I don't understand if it will send all of my personal data, like photos, contacts and other stuff to other devices if I use iCloud for syncing. They all have their own Apple ID names. The description under the option isn't clear enough to understand on which basis it decides whether it should send my personal information to my sister's iPad or my other sister's iPhone. Will they see my photo stream or messages or something? Does iCloud think of those devices as if they are mine if we use the same WiFi network? Please make it clear for me.