@lah, My sincerest condolences on the death of your little brother. COVID has complicated every aspect of our lives and none more so than those of being unable to grieve in the usually accepted manner and with rituals so many of us have depended upon until now.
I am so sorry you are going through these very turbulent, unsettling times due to your husband's changeable behavior during this battle you are both daily confronting and trying to deal with as a result of his cancer.
I recently lost my dearest friend of decades and am still reeling from the shock and reality of her death. During the months leading up to her final days, I was often frustrated and even resentful by the behaviors of both her guy and my friend. They were passive when I encouraged them to be much more proactive about her immediate health decisions, their changing of legal documents like wills, durable power of attorney, and living will, etc. Her protracted illness and their ages and mild mannered natures all contributed to almost unendurable family difficulties toward the end of her life.
Long a primary family caregiver, I can identify especially with your feelings of helplessness, confusion and distress in wanting to help but being rebuffed as you deal with your husband's sometimes unpredictable behavior.
My inability to be physically present or to have my friends act sooner on some issues that could have spared later grief has been incredibly hard for a "doer" who cares so much about their welfare.
Maybe it might help in some small way if you can tell yourself as I did myself many, many times that some of this hurtful behavior or inability to take action is all a part of the daily nightmare being experienced by these dearest ones meeting the new everyday challenges and changes in their lives.
Being a very sensitive person, it is harder for me than many not to take things too personally. Maybe reminding yourself that your husband is striking out at the person who he knows loves him best will help because we only strike out at those we feel closest to and safest with?
Our situations are far different but I want you to know that I am thinking of you and your beloved during this most stressful of times in your lives.