Hi LStrayed

I'm sorry you are going through this - it sounds like an incredibly heavy load - too much to have time to look after your own well-being.
Before his Dad got really sick he made my husband promise to take care of his mom and ADULT sisters!
What does your H think about this? Does
he want to take this on? Does he believe it is his responsibility, or does he feel resentment, or that it was an unfair demand by his father? (I'm assuming by your language that it was a demand, and not something your H volunteered to.)
Are you and your H both feeling the same, or do you and H have different feelings about how much he can be available for all those family issues (and still be available for his own family)?
When my mom was 14, her mother died from cancer, but before she died, she "made" my mother (14 yrs old), promise to always take care of her 8 year old sister. Their father was a horrible abuser (physically, sexually, emotionally). My mom did the best she could (she's uBPD), but decades ago she told me her mother should have never "made" her make a promise like that because it was unfair. I have to agree. It's FOGing, rather than a decision made of one's own free will. In your H's case, his siblings are adults. Seems to me those adults have a free will to exercise their own autonomy, even when the decisions made may be bad
or unhealthy ones.