You can turn off photo stream on one device without effecting the others. If you want to keep the photo stream photos on the device you are going to turn it off on, you will need to same them to your camera roll before doing so. To do this open the my photo stream album, tapping Select, tapping the photos, tap the share icon (box with upward facing arrow), then tapping Save to Camera Roll. Then go to Settings>iCloud>Photos and turn off My Photo Stream. This will delete the photo stream photos from this device, but not the others (and you already saved copies of these photos to your camera roll so they will still be on your device).
The other two iPads that are signed into your iCloud account with photo stream enabled will still be sharing the same photo stream but you will no longer see it, and your photos will no longer be added to the stream. They can still share photos with you by adding them to a shared stream and inviting you as a subscriber (as explained here: http://help.apple.com/icloud/#/mmc0cd7e99).