What should we do to ensure mother is safe?

I am the primary care for my elderly(90) mother who is a widow. Prior to becoming a widow she had two dogs. Both dogs died and after their death she finally told us that she fell several times but her husband was able to help her. Several years ago we cleaned out mothers house (borderline horder) and found animal feces a year after the dogs had died. We were able to get mother into a new Senior home close to us. My mother called my brother's son's wife the other day and asked her to take her to get a cat. This family member did not contact me or my brother to see if we thought it was alright. It should be noted that the last time this person saw my mother was in March and prior to that it was in January for 1 hour. The family members do not have any plans to help with mother or the cat.
I am concerned for my mothers safety after alot of hard work and daily visits to help mother is finally in a safe clean environment. I do not want to deal with a cat and mother is not capable of handling a cat. Which she proved when the cat escaped and mother ran outside almost falling and screaming I lost my cat. The person who got the cat of course was not available to help. Of course the cat came back.
I am heart sick but my brother is no help he does not want to upset his daughter-in-law. It should be noted he only shows up once a week for a few hours and is planning two vacations this summer along with his family lasting 10 days each.
How would you handle this?