There is a lot you can do to prepare for the inevitable and NOT to leave a mess for someone else to have to face. Amazon and AARP have several books/workbooks to choose from to guide you through getting everything in order and laid out for that next person, whether a family member, friend, or attorney.
If you expect to eventually pass in the community you now live in, make an appointment with a local funeral home and do the prepaid planning. The staff person will lead you through all the important questions of what you want and when the time comes, whether you are in the hospital, at home, in a facility- they will be called and will come and everything will be done as you planned. This takes a HUGE burden off the someone who will be stepping up.
Google Elder Law attorneys and make an appointment. If you don’t have a will, make one. If you do, review it and update as needed.
Call the customer service numbers of your assets (IRAs, CDs,401Ks, brokerage accounts) and put everything you can as POD (payable upon death) or TOD (transfer on death) to the beneficiaries of your choice. This way these assets don’t go into probate.
Commit to just one hour each day to clean closets, clean the attic, clean the basement. Take clothes you never wear, small appliances you never use, and tchotchkes to Goodwill. Give old tools away, etc, etc
If you own your home, make a plan for getting the house as ready as possible for eventual sale- gutters falling down? Furnace or a/c needs to be replaced? It’s been years since the rooms have been painted? Look around with a critical eye, ask a local realtor to view the house and make recommendations, start with what you can afford but don’t stop!
Finally, I hear your hurt that your mom has chosen your brother-in-law to handle her affairs, but of course, it’s her choice. If you see what you think is elder financial, emotional, or physical abuse, you can anonymously report this to your county Area Agency on Aging and they will investigate.
It is also understandable that in a situation like this for a person to have uncomfortable thoughts of “what about me?”. For your own mental well-being, concentrate on Judge Judy’s dictum- “Don’t be addicted to OPM”, say it quickly- sounds like opium, but stands for “Other People’s Money”. I am the younger sister of a much-favored older brother. Keeping this in mind really helped me keep a positive, cheerful attitude, “Que sera, sera”!