Is it permissible for the mother and sisters to clean and wash the girl the night before her wedding?

If the cleaning and washing are for parts other than the 'awrah (private parts), and there is no exposure of the 'awrah, then there is no harm in it. However, if it involves exposing the 'awrah or directly touching it, then it is not permissible due to the saying of the Prophet (peace be upon him): "Guard your 'awrah except from your wife or what your right hand possesses," and the statement of An-Nawawi: "It is forbidden for him to entrust it to anyone else except his wife or his female slave."