Family "sharing" - it's very secretive isn't it?

I dont use Apples Mail app on my iPad, preferring Gmail instead (who wouldn't!) - I don't own a Mac, just Windows PC running Windows 8.

I get an invite to view a family sharing group of pictures but on my ipad and and my windows PC I just get "iCloud Photo Sharing is not available for this device"

So, am I being punished for not using a pure Apple system throughout my life...? I just cant get any sense out the idea of family "sharing" - it seems to be just the opposite!

Any help - Im keen to see what has been apparently shared with me but seem to be blinded by Apple....

Thanks