@JaninaDuszejko
Being 53 is no excuse, I'm 51 and have a 10yo, I have a friend who had all her 3DC in her 40s and holds down a senior management job in an international company. I'm sure she finds a 6yo hard work (because they just are) but it would make such a massive difference to you if she looked after your DC for, e.g. 1 night a week. You sound like you are on your knees.
This kind of thing rankles me.
Just because someone is in good health, and bright eyed and bushy tailed, and works loads of hours, and is able to run marathons blah blah blah, at 53, that doesn't follow that someone else who's the same age can do the same.
Some people have physical health issues at that age, some have mental health issues, some have social anxiety, and some are actually too busy - ya know with their job - or other children living at home.
And in these probably fictional scenarios, there is ALWAYS a middle aged woman who had ALL of her kids in her 40s, who is a high flying executive for an 'international company.' Is it Esther Rantzen?
Or is it, as I suspect, someone who's a manager at the West Acton branch of McDonalds?
I am sorry you are struggling @changingstreets and it does all sound shit, but your mother isn't obliged to help you. Sounds like she has enough on her plate running her own home, and with your siblings still living there. I also cannot see a problem with her 'not wanting to go out to work.' She has kids still at home.
What is wrong with a woman in her 50s 'not going out to work' when they have kids still at home? Your dad sends money to her, but why shouldn't he? HE doesn't appear to be the one looking after HIS children. Also, why are you not denigrating your dad for not helping? Why just your mother?
She could occasionally offer to help you though I guess. It does seem a little harsh not to, just a couple of times a month even. I am on the fence a little. Leaning more towards being on your mother's side, but still seeing your point a bit.
I can't offer any real advice, but as @IncompleteSenten said, you know what to do when she is elderly and infirm and needs help. Just refuse.