From my experience before I retired, they may not believe the children but they are required to take the allegation seriously. My thoughts are.... has the husband been formally assessed as lacking in capacity to make his own decisions? If so who by and when?
I think the hospital feels itself (well hospitals can't feel but you know what I mean....) to be caught in the middle of this. Abuse allegations of vulnerable people are handled by Social Services and not by Health but health have certain protection responsibilities so if he is adjudged as vulnerable and lacking in capacity then they can't just wash their hands. Hence their decision to get him off the premises once he is fit to leave. As well as a solicitor, she should talk to Social Services about the allegations, as if there is no POA, then it is they who will be responsible for the man's ongoing care and for sorting out the allegations including identifying what the abuse consists of and what evidence there is that it happened. Accusers can't just say someone is abused, they have to say what the abuse was and what evidence there is. Your friend should make every effort to be seen as the reasonable one, to agree for instance that she will never be left alone with her husband for the time being; to co-operate with his temporaray placement in care, to STAY CALM yes that will be hard. She should not give any access to his finances or to amnything else. I am not sure what good having the will would be unless they intend to destroy it. Come to that, if he goes into care, I am assuming the couple have money, after the 6 week set aside he will need to contribute to his funding which will eat up any legacy they are expecting.
I should also say that a lovely bloke I knew many years ago who appeared devoted to his disabled wife turned out to have abused her (hit her) and also was a proven paedophile.....so you do never know.