I think it is them. Oshine is acting as surrogate mother to Silvestre which is a very sensible arrangement and will benefit him in future, but its also the first example that I've ever come across where a Bornean female is 'rearing' a Sumatran baby.
I think it has benefitted her enormously too. Her old life, although not natural for an orangutan and not doing her any good was 'luxurious' compared to what she has now. Who'd find it easy to swap helping yourself from the fridge and junk food for healthy veg and a limited calorie diet. Silvestre has given her something to help the transition to a new life.
Oshine was in a bad state before Monkeyworld took her on. She was absolutely gross- the most overweight Orang I've ever seen and I've seen a few of those!