splitting up a family

I currently have a family of four chinchillas, dad, mum, son who is 1 1/2 and a six month old girl. we no longer have time to look after them properly but no one wants to buy them. The pet shop will only take two and I don't know the nicest way to split them up. Ideally I would like to keep dad and daughter but am afraid they will continue to breed. any suggestions