"a big mess" is pretty much the definition of family life, isn't it?

That said, there comes a time when it's necessary to assert yourself. I think, for you, it might be important to start doing this now.

I hate doing this, since I'm probably a fair bit older than you and I don't want to sound like some old codger laying down the law. Even if that's who I am and what I'm doing! But I am quite literally speaking from experience.

30-40 years ago, I was being ignored as the 'black sheep' and my brother was the favoured son.

20 years ago, things changed. I was welcome again, and Chris was beginning the process of distancing himself from our parents as he already had from me. Unfortunately, Mum still believed she could get her way with me by shouting me down or appealing to Dad. Now before, I would have simply walked away again. But, I knew that in another 10 or 20 years, they were going to need support. I knew that there was no way I could effectively help them unless it was understood that I was in charge, because Dad freely admitted to me that the world was changing so fast that he no longer felt confident in keeping on top of things. So I put my foot down. There was a lot of shouting, screaming and crying at first. But in the end Mum realised she was on a hiding to nothing. The only thing I was never able to overcome until too late was her resistance to moving closer to us.

Now your mum is in a life-change process. She may blossom, she may soldier on, or she may go into her own decline. What is certain, given current life-expectancy and the attendant issues, is that at some point she will become too frail physically or mentally to take care of herself. At that point, which of you is going to be expected to look after her (by which I mean see to it that she is in the right sort of accommodation, with the proper care, manage her finances, etc)? I get a feeling that it won't be your sister! If that's the case, then you need to start positioning yourself, not as the dutiful daughter, but as the gaffer! Because if you don't, you're going to spend a lot of time being walked on, and if I'm any judge, you've already had a bellyful of that! Might be worth having a word or two (I can think of two right away, the second being 'off') with your sister as well.

OK I'm done. You have a perfect right to tell this grumpy, cynical old git to go forth and multiply. I wouldn't blame you if you do. But this is sincerely meant and based on evidence you've given me. There's no malice here, just respect.