Im afraid of losing people

I dont know how to feel in front of my mom when she explains to me that she’s having surgery and that she may have cancer as well. I wanna say loving things to her that i know would make her tear up but i feel like thats the equivalent of saying my goodbyes before she possibly dies. I haven’t acted worried in front of her lately and its because i want her to know i believe everything will be alright. She will die someday just like everyone else on Earth but I don’t want it to be soon so I am acting like there’s no risk. But i know for certain that there is a chance that she could die within the next few years, maybe months. And this is why i feel guilty for not showing her how worried i am. I kinda got mad at her a couple days ago because of how she kept talking like she was already dead. She was mentioning how she wanted her coffin to look like. And that’s when i sort of raised my voice and told her not to talk like that. I told her that she was strong and that she doesnt know for a fact that this will kill her yet. I don’t think i can handle the burial scene too well. If i dont show up for that day its not out of hate but rather out of fear. It especially frustrates me knowing how all my 5 siblings will feel. I’ve never seen my oldest brother cry and i dont want to. I dont wanna be seen crying neither when it does happen. Hopefully my family members don’t take it the wrong way when she takes her last breath and i struggle to hold back my tears. It’s not that i aint sad, its just that i wanna be strong for her when she dies. Sometimes i wish I didnt have such a big family cuz I know they’re all gonna die. I know we’re not immortal but still…life seems short for what it is.  I hope i die before all my brothers do.