I was thinking when she was talking about asking Yo and D if they could take them to the airport "if they have nothing better to do and we will pay them", that such close friends would usually have offered without being asked. I know it's quite a distance but I would do it for friends (and have done) especially if they had said how much luggage they would be struggling with plus some young children. But then I realised that's because I know my friends would offer to do the same for me if they could at the time, and Chris and Sarah have never done anything in return for Yo and D. Then there is also the fact that it's very difficult to arrange to help someone if they keep changing their plans every day as most people need some notice of being able to rearrange their own plans, take time off work.
It just adds to the whole feel of them being paid help rather than best friends. It's all one sided, and whilst Yo and D do what is asked of them, that's where it seems to end. They turn up whenever asked, they move vehicles when told to but have they ever said "We're driving nearby later, do you want to meet up for a quick lunch?" Has yo ever said to Sarah "I'm off work tomorrow, want to come round for some coffee and cake and have a catch up?"
I know they don't live close so meeting friends who live further away does usually result in a longer meet up due to someone having travelled, but Chris and Sarah don't actually have anything else to do anyway. I just don't see genuine every day friendship between any of them.