Please stop the thinking that it's your fault. It sounds as if you might have an overly severe conscience. Think about what's been done to you emotionally. You're seeing your therapist soon, aren't you?

Maybe you should ask for your meds to be tweaked for a short time while you
recouperate at an apartment of your own or with your brother in a home you two own together. If you and your brother get along, that's a much cheaper route to follow, simply because you will need to sign a lease if you decide to rent, and things
may change readily in the coming months.

A mother-in-law may not be the best one to confide in since it is her daughter who
is responsible for the problems. Most mothers are going to be very gentle with their
children's problems. A better source for you, in my view, is your grandmother who
has lived the longest and had the most experience with people (generally speaking, of course, of older people. Not all are wise, by any means, but chances are she might be.)

Good wishes.