I think the issue here is that your friends partner did not want another person moving in and possibly outliving his surviving spouse. Once the new partner was established as a resident in the house , no matter what the will says, it would be hard to get him out again if he chose to be difficult. There would need to be an eviction notice and if the 'new partner' declared that he had no where else to live a court may not grant an eviction notice.
If the daughters allowed him to move in his case would be pretty solid to stay there until he died. I am not sure on this we do need Barmaid for the legal view.