see here for their old cage:
http://www.zoochat.com/1956/old-chimpanzee-cage-355913/
The island is quite large but unfortunately has little in the way of climbing structures -- just the swinging ladder thing on the left. I did not see the chimps (they were inside their house at the rear) so I do not know how many there are, or how old they are
See here for my
http://www.zoochat.com/254/alipore-zoo-visit-15-feb-2014-a-355860/