My sibling and I are gainfully employed, educated and housed adults with the ability to look after ourselves and take financial responsibility for ourselves.
But what if you weren't ?
The thing is, costs of things these days is really expensive, especially housing.
If you are in below average/low wage jobs getting on the housing ladder is really difficult.
Not everyone has the capability to earn a fortune, or lives in an affordable area.
My guess is that the OPs children are about 50 years old if her mother died at 99. They are probably at the age where they are starting to think about their own retirement.
They have had enough time to see how difficult life is, and are in rented accommodation. My guess is they have figured out by now that inheritance is/was their last chance ticket to a better lifestyle. And that expectation has now been crushed. At least for the foreseeable future, unless they expect to inherit from other family members.
There are an increasing amount of threads on here about inheritances. Why ? Because in todays world it's becoming increasingly difficult to have a lifestyle without one.
It's easy to say ah well, look how entitled they are, from a position of having a great job, house and your own significant inheritance. When it is your hopes and expectations being crushed though it's a different issue.
I don't think here that the children have been well behaved, especially when you consider they are quite old themselves (you might expect differently from younger kids) but I think it's reasonable to question whether they were always made properly aware of the situation and that their expectations were properly managed. There is maybe a lesson in there.
I hope over time the children can overcome their disappointment and realise they are being unreasonable and that both parties can have a good relationship going forwards.
I don't see that estrangement and anger leaving all your money to charity as some people have suggested is a positive outcome for either side.