They've been there simnce 2009 according to Zootierliste - I honestly can't remember for myself if there were more than these two (saw a lot of animals that day!) but there were only 1.1 in November 2010 (again taken from Zootierliste).
Thanks. I hope Berlin zoogoers enjoy them while they can. I think they will not be able to replace them when they die. That is true for other zoos with Hamlyn's in Europe nowadays too- unless breeding suddenly increases.