I get what you're saying. It's difficult for others in our family to understand the full nature, and throes of depression & suicidal thoughts, or other kinds of severe mental illnesses, unless they've lived through, or with them - themselves.
It's so very easy, instead, to pass judgement... & "to think," that you know it all~
I felt like this (once) & I did that, and it took care of, or remedied it. Why can't you, or why can't you find your similar answer, as did I - once upon a time.
I'm guessing your sisters have families of their own. This only complicates, or exacerbates the dilemma, of forming some kind of ...bond? Or way in which you feel you have the right to connect with them (for we often feel that we are being selfish, by burdening them with our troubles). So if they have their hands tied up in other affairs, or family members of their own. If for no better reason, then. Than lack of available time for you, or us. We can't be a bother to them. And it is also (more) convenient for them. To not go to that extra mile that they otherwise might, in order to reach out & see how it is, that we are really doing? Truly!
Excuses, reasons, it doesn't matter which. Or even if it is none of those. That the barrier exists, or the gap is present, is all that matters, and all that remains, in reality. Maybe there is some way to change this dynamic in your relationship with your siblings? Perhaps this funeral for your Brother, might present a turning point, or a moment of crystallization, or crystal clear thinking, or bringing things into more laser focus. In terms of just how precious & fragile life is. We can be here & present in one moment, and gone in the next~*
Perhaps they will be exceeding good to, or for you. Regardless of reason, or motivation. That would be wonderful. Let's hope negative family history doesn't present itself.
I have been dealing with, or struggling to deal with a grief of a different kind or manner for about two years. Very/highly unsuccessfully, you might say. Recently I've stumbled across a new book, on how to in his opinion anyway, based on some experience with dying patients & their families in side of hospitals settings (he was a chaplain, I guess - & I'm not all that religious) / but his alternative or unconventional take, has been really the first thing that has helped me to open my eyes & to try to see things in a different light. That said, it's taken a while to get to here (nearly two years). And so, I don't know how noteworthy or useful/& valuable it would be, for someone in your position. But if it sounds like something you might be interested in checking out, at some future point, should you find yourself struggling to cope. I can leave a link here, so you know what it is (that speaks to me, have no idea or clue, if it would do so for you). :^)
https://www.amazon.com/As-Long-You-Need-Permission-ebook/dp/B0CD3PXCRK
https://www.barnesandnoble.com/w/as-long-as-you-need-j-s-park/1143709777