Pupuce, this is a really hard one, and I know because I have had very similar problems with my mother. For many years she's been slowly letting the house slide into a chaotic decline (while, curiously, continually buying hoovers), drinking and chain smoking - all as the result of depression. And, like your father, she's also reliant on me for money, for complicated family history reasons.
While things have now got a bit better for her, I'm not sure how much of this is to do with me - so whether I can give you any suggestions that will work for you, I don't know. But here goes.
My immediate response is always to rush in and try and sort things out, tidy up, buy shelves, throw things away etc etc etc. But it was only when I went into counselling that I realised that this was making things worse not better, because it made her feel less competent and more useless. What my counsellor suggested was to spend more time just talking to her, rather than trying to 'fix' her. So I tried to go round a bit more (not sure whether this is an option for you, whether you are even in the same country), not to try and sort it out, and to try and ring in the morning, when she might be making sense (like you, ringing after 7 is impossible).
And gradually she has sought help for the drinking and the depression - although, like I say, how much of this she would have done on her own anyway, I don't know. But it took me a LOT of asking, repeatedly, gently, explaining how much it upset me to see her in this kind of state. I also think that my talking to her about my own counselling helped, as it enabled her to see that she wasn't the only one not coping, and so she wasn't a 'failure' if she went. But all of this only after years of resistance, refusing Alcoholics Anonymous, refusing to acknowledge any problem, having 'bad' reactions to anti-depressants etc etc etc.
I think the other thing that you have to do is accept that, in the end, you can't fix it. While things have got better - my mother is more cheerful, drinking less, looks better, does voluntary work - the garden was still coming in through the windows last time I visited. But she's an adult and that is her choice.
So I think in the end, inasmuch as I have a conclusion, I agree with Missycocker - the only thing you can do is change your own behaviour and hope that this makes a difference, but accept that it may not. And like you, incidentally, grandchildren may not be the answer for my mother - she seems to be finding it quite hard to deal with my pregnancy - her first grandchild. But her first child was a stillbirth, and this was the point at which things started to go wrong for her, so it brings back painful memories for her.
Not sure if this helps, but you are not the only one by any means.