My Parents want to leave me all their money with the exception I support my sister. What are the disadvantages of this?

My sister is a bit of a basket case. No mental illness or anything just very stupid with money. Over the years my parents have had to bail her out lots of times. She's not well off, works a minimum wage job and gets universal credit.

My parents are currently planning their estate and have sprung on us that they do not want to leave her any money as they think she will immediate blow it on stupid stuff and have nothing to support herself. What they want to do instead is leave it all to me with the expectation that I pay for certain expenses for her and help her out. Essentially I would have to ringfence 50% of it and keep that to use for her. They think the advantage of this as well is that she would keep her universal credit as well as no money would be in her name.

I have a lot of concerns about this.firsrly I'm not really comfortable being my sister's keeper for the rest of my natural life. I think it'll fuck our relationship up if I have to vet every purchase she makes etc.

But what I'm looking for are the legal/financial Implications of this. What am I not thinking of that would cause this to be a bad idea and I can present to my parents as to why they shouldn't do this.