I'm interested in learning some of the Executive Skills I seemed to not pick up as a child/teenager and ended up getting a parenting book about it, to see if I could parent myself into managing to do things. The book I went for was "Smart but Scattered" (its American but I'm sure there will be other ones out there if it doesn't appeal to you).
Anyway, it talks about meeting the child where they are in terms of their skills even if they are behind their peers, and gradually helping them to need less support. Its recognising that each task and area of their lives involves a set of skills that needs to be worked on.
So from memory, the general approach is to appreciate that often a task they are struggling with which seems obvious is actually a series of tasks which require certain skills that they are lacking, you break the task down into smaller chunks which initially need a lot of supervision, then fading that supervision and giving them the skills to manage their own tasks.
So tidying the room. You'd sit down together and make a check list of all the tasks that need to be done to tidy the bedroom (e.g. put dirty clothes in the wash basket, clean clothes folded/hung away, put books on the shelves, return dishes to the kitchen, dust, vacum - each task in however much detail it needs to be for the child). Then you go through it at whatever their current ability allows - which might mean lots of supervising and encouragement, doing it together etc. Gradually you move from helping a lot, to prompting them to look at what's next on the list themselves and eventually just checking that it's been done at the end.
It deals with all sorts of issues, not just getting them to keep their room tidy and organising themselves. I don't know what level your daughter would be at or capable of achieving, but you start with where she is and just build on it from there.
The sibling stuff is more complicated, wanting to be fair to two teens with different needs must be difficult. But they wont be measuring themselves against each other for ever, they both need to develop the skills they can.
Its worth saying that the approach in the book (breaking things down into smaller tasks, supervising them then fading the supervision) isn't just for kids with particular difficulties, it can help NT children learn things they might just have missed.