Responsibilities of parents regards providing for an adult child with a major disability post their death

I am after peoples opinion in regard to if they would deem it to be a general community expectation, that parents whom have the financial means, have a responsibility to ensure that adequate stable long-term accommodation is available, once they have both passed away, for an adult child with a major mental health condition? I have become aware that my parents have taken no steps to do this for my sister, and she does not have the financial means now or in the future to purchase a home for such security, and thus my parents are leaving such to chance, and with the unspoken expectation that if any problems occur that my brother's and I will sort it out?

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My husband and I have a 22 year old daughter whom has Cerebral Palsy, an only child and our primary focus. We are taking steps to ensure our daughter has adequate stable long-term accommodation once we are no longer here, but will not be in a position financially to assist in purchasing a home if by chance my parents estate does not leave enough (or anything) to secure housing for my sister - and I doubt my brother's will either, as they have adult children themselves whom may need assistance in purchasing their own homes in the future. For us, making arrangements to secure our daughter’s future accommodation has been about finding ways that will help to ensure that her future home cannot be clawed at by the government for their use in funding our future aged care or such.

I have no problems with my parents 'spending more on one child than another' so that they can make adequate secure accommodation arrangements for my sister for when they are no longer here. But I do have a problem with them doing nothing as this could potentially end up with them not leaving enough (or nothing) to bequest for the purpose of being able to purchase a home for my sister, and thus leaving a potentially difficult distressing situation for their other children to manage. Regards my sister, she has a longterm chronic mental health condition, lives at home with my parents, is and has been on a Disability Pension for nearly 15 years, where such pension is likely to continue for the remainder of her life, has no real future earning ability that will enable her to purchase a home and very little in the way of superannuation.

To put my parents financial situation into a bit more perspective, they are self funded retirees, who retired about ten years ago each with superannuation, have 3 investment properties and received around five years ago an inheritance of just over a million dollars (in which maybe a ¼ was used to purchase their 3rd investment property). To me, my parents have rather indulgent expensive spending habits. Their current financial position will require them to sell an investment property in the next year or two for the purpose of living on, as their supper will run out by that time and it would seem little in the way of liquid assets is left. I have no problem with people spending their hard earned money in their retirement, but I fail to understand how a parent could fail to even consider using a small fraction of a large inheritance to financially secure long term accommodation for an adult child with a major disability, thus leaving the accommodation outcomes for that child to chance. I see my parents behaviour in regards this issue as being irresponsible and self-centered, and this makes me angry and disappointed with them. Are my expectations in regards to what I would expect the average parent to be able to do under similar circumstances to my parents unrealistic? I fail to believe that my husband and I are operating to higher standards, and that it is unrealistic to expect my parents or others to operate to such standards - such sounds rather condescending and seems simply an excuse or cop-out to me.