Here is the answer you all want about Photostream. If you have it selected on, your pictures will go to the cloud for thirty days, and will remain on your phone in Photostream and also will be in Camera Roll. If you turn Photostream off, select the bright red Delete Photos at the bottom of the screen. Leave Photostream off. When you go back to your photo albums, Photostream is gone and so are your pictures. But if you select Photostream back on again, the pictures arrive back on your phone. So this is what you do if you want to keep several of your Photostream pictures for good and get rid of the rest.
1. Select the Photostream album.
2. Tap on the picture you like and want to keep.
3. Hit the lower left swirl arrow and it will give you a choice of what you want to do. Save it to Camera Roll, or wherever you want it to go. Do this to each picturre each you want to keep. Now you have a permanent picture on your phone in Camera Roll, but you can easily delete pictures from Camera Roll at any time, with no cloud involvement.
4. Turn off the Photostream option and select Delete Photos.
5. Now go to your computer, login to icloud.com Now, look up in the upper right hand corner and click on your username.
6. Select Advanced. Choose to reset contents of Photostream, which will delete ALL photos in your Photostream holding account, and resets it to zero, the maximum I believe to be 1000. They are gone.
7. Just to make sure, go back to your iphone and reselect Photostream on.
8. Now go to photos, and you will Photostream on with just a puffy cloud, no photos. They are gone for good, but you have the ones you wanted safely in your Camera Roll.
Not a perfect method, but the best I can see on how to handle this feature on your iipads and iphones.