Something similar happened to me. My parents died 2 months apart a couple of years ago. My older brother died last year and he was the last of my family. It's been very hard at times knowing there's no one left but me but I've built a network family and that helps.
Wow. Sorry to hear that. I have 7 siblings. 2 have died along with Mom and Dad. I cherish my family. Can't imagine losing them all.
I am so sorry to hear about your loses...my goodness, you have been through a lot as well.
My sympathy to you.
sleuth