What to do about BIL who is making MIL agitated?

My MIL lived with us starting last July, I agreed to be her care-taker. I am medically retired due to back problems, but at the time she was ambulatory. In Oct/Nov, she became ill with multiple UTI and at that point needed assistance up and down, in the toilet, etc. I was unable to continue care due to my back issues. In addition, her dementia became worse. We discussed with my husband's brothers the need to place her. Her income is such that we could not afford to place her in a memory care facility, but I found a very nice board and care facility nearby. She is on hospice and seen on a regular basis by nurses and the facility has LVN staff. My husband's oldest brother did not see her during this time. I developed pneumonia two days after Christmas and was unable to see her for approximately one month. When I was better, we took my husband's brother to see her at the facility (he had not bothered to see her for 3 months). Shortly after this he began visiting her weekly. He has accused staff of over medicating her, that she wasn't this bad when he went in to the facility (she was, he had not seen her for at least one month). Now he is prompting her to say she does not like it there (but she cannot tell us why) and he is prompting her to guilt us into taking her back into our house even though I am unable to care for her. I don't known what to do to make him stop this behavior. And no, non of us has POA. I am just so frustrated at this man!