Brother in Hospital/Controlling sister-in-law

For the last year, my brother in England has been going through treatment for an aggressive form of terminal brain cancer, which has largely been unsuccessful. My parents and I live in the US and have been reliant on his wife to keep us posted on his health and assist him as needed. Last month, we received a call from her that my brother has been rehospitalised, and we need to come over immediately. Since then, he has been in palliative care, and unable to speak, move, or eat. His wife has stayed with him in the hospital every day and night, and We’ve stayed in London for the month, and are going into our second month, depleting our savings to stay in rentals. There has been no change to his condition, but his wife has told us we cannot do two visits a day anymore, and that we can only visit once a day for one hour during a pre-determined and supervised time, due to his energy levels. This is disappointing yet fair.

Since then though, she has been increasingly demanding, telling us we cannot touch him, critiquing what we say to him (“don’t say how proud you are of him like he’s dying”), chastising us for discussing food since he cannot eat (while she’s eating a hot, odorous, meal in the room), and much more. We also cannot have private visits with him, and she refuses to leave us with him. To be clear, while my brother enjoys his space, our parents are loving, have supported him all his life, and put him through university on their own dime, without asking for anything in return. Recently, my mom asked if our sister-in-law would like to have the night off, and my mom could stay in the hospital with him, to which the wife said absolutely not, my brother would not want that. We then find out that when our sister-in-law goes out for dinner, her mother stays with my brother. We offered to stay with him while she goes out, and she said that my brother would prefer to be with the mother-in-law.

What is the worst part is how she communicates. She makes no small talk with us, and has gone from being short to outright rude and insulting. One day his oxygen dipped low and she said we’re probably sucking all the air out of the room. Another day, there was a bald spot on his arm, and she said we probably rubbed it bald with our touching. I didn’t initially mind the boundary setting, but her tone has taken on a purely spiteful and aggressive attitude. All while being pleasant with nurses and doctors. Our visits are stressful now, as we have to mind every word we say during these supervised visits, and she watches our every move, and acts aggressive. We feel unwanted here, but feel it is important to spend these moments with my brother/my parents’ son. 

Has anyone else had similar experiences with the spouse taking full control of the situation and being incredibly aggresive towards family? I doubt there’s any chance of mediation. Should we just go home to the States? I just feel lost here, and stuck between feeling like I want to be here for my brother, but honoring these boundaries I never knew existed