That all sounds REALLY tough, Jer, and you are to be commended for your love and patience. Just a thought: is it possible your sister only wants to see her husband because she's lonely and besides you and mom (who just can't be there ALL the time, of course!), there's only him? If so, a small pet might would alleviate some of that but I can't imagine who would care for it. Is it possible that you can check with the home or perhaps a charitable organization that might arrange for a volunteer or perhaps a high school kid who's considering the medical field or something to routinely visit her, say a couple/few times a week? I know there are some out there that do that.
In the meantime, I can totally relate to how frustrating this all MUST be for you (caring for the sick can be tough!)... but it's GOT to be terrifying for her, to be a body that has betrayed her and left her at the mercy of others, even someone who can't care for as she needs). And now she has to "hide" her husband (because she's knows he's not good for her at all!)... so imagine the guilt on top of the pain and fear. You poor folks, truly!
Just some thoughts and, again, she is very fortunate to have you as her brother.
A doulos of Christ,
SA