Photostream different on different devices using same iCloud account !

I'm having a very frustrating issue with Photostream between my devices.

Pictures taken on my iPad Air appear almost instantly in the Photo Stream folder on my iPhone 6 Plus. However, pictures taken on the iPhone 6 do not appear on the iPad and the iPad does not have a Photo Stream folder to access ! I have tried turning Photo Stream on and off on both devices but to no avail.

The other strange thing is that when accessing "Photo Library" on my Apple TV, the pictures displayed are from the iPhone Photo Stream folder only with nothing shown from my iPad. However, when I access iCloud using a web browser on my PC, the pictures shown under Photo Stream are the ones from my iPad "All Photos" folder and none of these appear in my iPhone Photo Stream folder. All devices are using exactly the same iCloud account !

I've been trying to resolve this problem for weeks but without success.

Any helpful advice would be much appreciated. Thank you.