Adult son and wife both working full time will live with us for around 6 months to save for house deposit. Around £2600 take home pay between them, only outgoing is a small car. Our overall household Bill's and food is around £2400 a month, around half of our monthly income. They will not have to buy any food and I will be making all meals. What is a reasonable contribution from them? (We also will be giving them half towards their desposit)