@SunsetSenora This thread was never going to go well, because people with wonderful relationships, (or even decent/normal ones) with siblings, can't possibly know what it's like to be estranged from them, and to have toxic, or non-existent relationships. Sometimes it IS because a parent has been a total shit, sometimes, it's because the sibling is just a self-centred, narcissistic arsehole.
Maybe your siblings did have a different/not great relationship with your mother, (that you weren't aware of,) it's hard to know. I know a number of people who are estranged from their mother because of personal, sensitive issues and reasons, and they don't talk about it because it's hurtful.
And their sibling(s) who think their mother is great, can't fathom what their problem, is and why they don't get on with mother. They have had to give their sibling a wide berth because it's so hurtful that they get on with the mother, and they, themselves don't.
But also, as I said, some people are just arseholes, and the parent has done nothing wrong. And I also know a few families where one sibling is the main support for the mother, and the other siblings are just selfish self-centred individuals who rarely visit, and in some cases, have moved away, and have not been in touch for YEARS. No real massive rift, they just can't be arsed.
All that said, if (to the best of your knowledge,) it's a case of your siblings not bothering with your mother, and not being in touch for years, and you being the main caregiver, and main source of support for the past decade or more, YANBU to not contact them to inform them of her death.
IMO, if someone (not just relatives, but old friends, colleagues, and acquaintances,) have not been in touch with someone for more than a decade, they don't deserve to be told that person has died.
If they 'care' enough to turn up at someone's funeral, and think they need to turn up 'to show their respect' then why were they not arsed with them when they were alive? Why did they not 'show their respect' then?
Whether your siblings DESERVE to be told their mother is dead, is debateable, but you don't necessarily have to be the one to inform them. If they cared about her enough, they'd have stayed in touch, and would know she had died.
I am sorry you're going through all this, and I wish you well.