I am thinking of doing the 5:2 and so is my DH.
My main worry is how I would cope having to see my kids eating their usual peanut butter on toast after school and then having to cook them a normal meal for tea. I usually cook them a proper meal from scratch and I often do this from 5-6pm while they're in the kitchen doing homework/chatting then we all eat together at 6. Surely this would be a nightmare if I was fasting. I'm not sure I'd cope twice a week.
Also do people swap the days round? I imagine you look in your diary the week before and plan the best days for fasting I.e busy days at work and days with no social plans for evening?