My current situation is somewhat similar to yours if not quite as extreme. I grew up with 3 sisters down in SO. CAL. until our parents retired and moved north to Washington state in 1990. Eventually all 4 of us relocated our families up here to be closer to our parents, as well as just getting the hell out of California.
Our dad died in 2001 of liver cancer, and then our mom died in 2010 from complications from diabetes. However, our older sister died in 2020 at the age of 64 from a massive infection in her spine. After this happened, our brother in law sold the house and moved to Arizona to be alone. Then 2 years ago both of my younger sisters moved to South Carolina to get out of Washington states crappy weather and lack of sunshine.
This has left me as the oldest member of my family in a state that I can't stand living in due to the weather and the political leadership here. We used to have family gatherings several times a year to celebrate b'days, mom's day, dad's day, etc. If we're lucky, we might see my sisters a couple of times a year now. I'm already dealing with chronic pain due to osteoarthritis and neuropathy, along with clinical depression. I've been "retired" for over 10 years now, but my wife is still working to support us, so I spend most of my time alone in the house everyday. Both of our kids and their families live locally, yet getting to spend time with them is like pulling hen's teeth. They always seem to have other plans, and it's obvious, to me anyway, that spending time with us isn't anywhere near a high priority of theirs.
So I feel like you in some ways, I'm the oldest living member of the family, but spend the vast majority of my time alone everyday, and it's not fun is it?