I don't know what things are like now in hospitals, but would Chris be able to stay with Sarah when she gives birth?
If he can, and they are on holiday and Sarah goes into labour, will they just leave Isabelle in charge of all the kids? Sarah could easily go in to labour early. What would they do with the chuldrun? Would he even find the nearest hospital? (I say near in the loosest sense as people have to travel miles to get to hospital in Cornwall). What would he do with the caravan? Dump it with the children in? Chris isn't going to miss out on filming the precious moments
It's one thing having Izzy babysit when there are adults in the house/garden to call on but another thing to leave her in charge by herself completely alone. She could have to watch them overnight etc if Sarah is in labour for a long time (though I'd imagine after that many it would just slide out). Isabelle seems sweet ("you only see 20 minutes of our day!!!!!") but doesn't seem to have any common sense or independence. I couldn't imagine leaving her in charge of Esme and Isla and especially not Jace for a prolonged period of time. Would she cope in an emergency?
Have they even thought of a plan for if Sarah goes into labour on holiday in a random place where they have no idea where to get medical help and nobody to call on to help then with childcare?