I am sorry to hear about your past. It sounds like one crisis on top of another. You should consider contacting a therapist who can focus on listening just to you and addressing your needs. Your attention has probably been on meeting the needs of others and this can lead one to feel drained. As far as your mother in law ignoring her tirades will lessen them over time. This can be attention seeking behavior and when she doesn't get the attention the payoff will disappear and eventually her nit picking. You may also investigate any services in your area that help care for the elderly. Services under Medicare for instance would at least help you take care of her.
You should commend yourself on raising considerate children. That is an important positive in your life. They did not become the people they are without your influence. Even if they are a little behind they are still achieving.
I would allow for private time for yourself despite the chaos that allows you to rewind and replenish yourself. A small amount of time every week should be devoted to you. Don't give everything to everyone.
Please provide positive feedback so I am compensated