mme,
You and your husband hang in there, did the Hospice your sister-in-law is with give you a pamphet called "Gone From My Sight" by Barbara Karnes? I found it helpful in knowing what to expect next.
You and your husband are wonderful to take your sister-in-law in, no one should be alone. I don't have kids so I often wonder who will take care of me if my husband is not around. One good thing is I have siblings and that is good.
Just take one day at a time, enjoy what time you and your husband have with her, I also view it as if the roles were reversed....I would want to be treated, loved and care for the same way.
Life is so precious and you and your husband also need to take care of yourselves.
God Bless.