Changing locks on inherited property that you do not own.

r/

Location: Victoria Australia

Ok so my grandmother recently passed away and she left her house, which was solely in her name to her two children my mother and uncle. My grandmothers husband has lived in the house with her for about 20 years and in her will she said he is allowed to remain in the residence until he is no longer able to or does not want to.

Today he decided to change the locks and now my mother can no longer gain access to the home. As the house was left to her and her brother in the will is “step-grandfather” allowed to change the locks since he does not own the home and the will states he is allowed to remain there. Any legal loopholes to get him out of the house?