Big solutions and small stress management tools.
Re: Big Solutions. You cannot be everyone's caregiver. If there is money to outsource to a care manager for mom, consider it. Find out what services your brother qualifies for with his disability. None of this is abandonment (as my mother would claim). You still visit, but you put your teen, yourself and your marriage before them. If there is backlash you remind yourself, if you end with a life-threatening illness you can't help anyone at all.
I do the typical little things often suggested for stress like exercise, outdoor time, etc., but before I came up with big sustainable solutions I was miserable, catching every virus and finding out about new health issues.
One thing that the backlash from outsourcing did was remove my guilt. The lack of empathy, dehumanization and entitlement showed me as well as the lack of gratitude for what I had done for years (for free) spoke volumes. I also remind myself I am mother before I am an adult daughter.