My heart goes out to you. I have been where you are. You MUST take care of yourself or there will be no one to help your mother-in-law! I found that sharing with my mom MY troubles and how I loved her, wanted to provide for her but how it was affecting ME mentally, physically, spiritually in every way. She began to take a new look at what was happening and more willing to consider other options. I also had to deal with spouse and family in the same way. I ended up taking a few days "off" to go away and visit "a sick friend" (me in a hotel room with a spa!) My family was left to care for mom the way I did with great notes from me on what must be done. After 3 days, they felt I was overworked! They didn't want to do it, especially after they realized what was done each day by me and they knew then it was a decision that needed to take place. As long as I kept the focus on me and what I had to go through instead of my mom where she felt she had to be on the defense, it worked out much better.
It was the decision to place my mother that ended me up in the job I have today! It is not an easy thing to do even when everyone agrees and is ready for it! Much worse when they can't see it.
I found for me, when I resented my brother for not helping me it was really myself I was mad at. I allowed them to back off and not help. It was my willingness to do EVERYTHING that helped them only visit sometimes because they knew I would handle it ALL. Once I said, "I can't do this anymore, so you need to come up with a different plan." They began to work with me.
Once my mom was placed in a community that could meet her needs AND mine. I was there more often visiting so we could just VISIT. My family came a little more often because they no longer felt pressure or guilt of not doing things themselves. They and I could see she was cared for and it was a big relief for us all.
May you be richly blessed for the tremendous job you've accomplished thus far and blessed further with understanding family members. I will remember you and your family in the day to day decisions that are upcoming.