On the death wish: Have you asked him where he wants to be buried?
What a Bastard. You Dad is/was in a near death state. Your brother is in life or death circumstances. And your husband is aggressively jealous of the empathy and care you have for your family members to the point of entering into competition with them. It is controlling and emotionally abusive. It denies you your truth of your own feelings.
Imho, also, he may see your attention to your brother and father as attention to another man...And is behaving as if you have betrayed your loyalty to him. Utterly devoid of any emotional intelligence. But yet...You have groveled and stroked him and he has dismissed your attentions as so much insincere lip service
! He has arrived at a mindset to compete with the other men in your life-being ever so narrow minded to ignore the obvious fact that they are family, not lovers!!
Imho, if you are sure he would never/has never had it in him to physically hurt you, then the only way he can see to utterly devastate you (and make no doubt: this is for punishment) is to destroy the thing you hold most dear-and that is your family. Hurt the children and through them, you (although it can be debated the dissolution of your family may be a good thing
in terms of the dc). He is making it clear that he can not tolerate you talking about (or thinking about) another man, even if it is your dad or brother. If you are going to stay with him, imho, you will need to have a strong boundary to never discuss your dad and brother with him or within his hearing. I believe that you will never get any support from your husband when your father eventually passes on, or any support for you (let alone your brother) as your brother endures the stresses and uncertainties of his diagnosis and treatments.
Looking into a crystal ball: I see you, demonchops, answering your husband's query as to how you dad is doing with a "He's fine" as you and all dc walk past, dressed in black, and out the door to your father's funeral.
So sorry you have to deal with this. My sister had similar.