Stiff (Deadly #3) by Morris Gleitzman

I thought my family were weird, but this lot left them for dead. Kids driving military trucks. Grown men wearing enough skin cream to moisturise an elephant. Compulsory afternoon tea. Little brothers who were forty years older than their big brothers. What did it all mean?

Amy and Sprocket are on a mission - to find her dad and his mum, rescue the baby from the Brats and uncover exactly what is going on inside the mysterious nudist colony. But the truth is even more terrifying than anything they imagined...