I am sooooo not an enlightened expert on this, so what I have to add is only an anecdote from one family, but fwiw, My primary advice is to go wi your gut feeling, whatever it is, about the best way to handle each situation.
When my mother died, her health declined slowly for a few years and then very rapidly over the course of two months. Even th we knew the end was semi-near -as in probably within the next year, when she died it was much sooner and more unexpected than we or her caretakers had anticipated. My children all loved her very much Althea we lived across a continent and they only saw her 1-2 times per year. The year she was declining we did not visit during the holidays because we had other commitments at home. She was unable to talk on the phone due to illness during those holidays, and this was unusual for our kids - they were used to skyline with family during birthdays etc. there was a lot of high-stress talking taking place among the adults in my family re my moms situation, but we kept that from our kids simply because it was the holiday and we wanted them to have a happy holiday. When my mom died soon after, we weren't with her. The kids hadn't had a chance to prepare for it or say goodbye, and they were definitely caught by surprise. Not what I would have anticipated as a desirable situation, but it worked out formy kids, and maybe even better than just ok. My dd who was the closest to her was of course hit hard, but knowing ahead of time would only have filled her life with anxiety and dread and also filled my life with having to deal with her anxiety at a time when I had an overload of adult anxiety and worries and planning etc to deal with. Even though it was sudden and they weren't prepared for it, we were able to work through the feelings and worries etc that my children experienced and it was (jmo, and just in this situation) less stressful than if we'd started working through it all before she died.
I would not have been able to fully predict ahead of time how grief over this one death would have Impacted each of my children even though I know them well. My dswas sooooooo upset and sad when he was younger and our elder
Y dog died - even though he never paid attention to her or played with her. He is very sensitive and I would have anticipated he would have been hit very hard by his grandmothers death but it didn't impact him in any extreme way. I think being older than when our dog died he was more understanding of aging and the impact it has and the reality of the natural end of life for us all. He absolutely understood the finality of death when our dog died but didn't have as much life experience at that time to out it into perspective. My older dd was very very very sad, but she would have been anyway. My youngest dd was more out of touch with what happened - she was worried about things like do the people who take care of her know she's dead rather than upset about her actually being dead. So if we'd had the time to prep yngest dd, we would have had time to reassure her that yes, the people who took care of her would know not to come to work the next day.... but realistically we could not have predicted that was something shed need reassurance about. We did fly our entire family to the funeral, which was helpful for our kids and more helpful for me - I had the people with me I care the most about at a time when I didn't want to be missing them.
So do the preparing that makes sense to you as the parent of your child, don't go so above and beyond that you have additional stress on top of having to deal with your loss and worries, and know that whatever approach you take, it will be ok.
I'm so sorry you are facing the loss of your mother in law and that your brother is fighting cancer. I will be thinking of each of you.
polarbear
Ps - I am replying on my iPad - hopefully there won't be too many odd spell-corrects
