Washroom below staircase

Uncle built a three storied house by sanctioned plan and willed each floor to each of his children. There is a small washroom built below staircase and this is not mentioned anywhere in the building sanction plan. All was going well until son staying on second floor expressed a need to use this wash area due to some painting works going on in his top floor. The ground floor owner was willed 'the entire ground floor' as per uncles will. The ground floor owner is objecting and has changed the wash room lock Is this right? Isnt the washroom common for all floors when required? Our understanding is that since it's not a sanctioned portion, it's not subject to contents of will. Ground floor owner has abused loudly and excessively