I will interpret your gratitude as license to infodump. (I have
many thoughts, and few parents-of-children to share them with.)
They're not going to be dependent on you their whole lives. They will be dependent on society, but so are the majority of neurotypical adults. If they're capable of interacting with the outside world, having deliberate hobbies, etc, then while they may need extra/different support with many aspects of life, there will be areas where they don't need the support that society offers ordinarily. (I cannot tell you what areas those will be, but I'm confident there will be some.) Autistic children become autistic adults but, as with anyone, they need opportunities to mature and learn life skills if they are to become competent autistic adults.
Don't assume that there's anything your daughters are incapable of. "Doesn't talk" doesn't mean "can't speak", which doesn't mean "can't understand speech", which doesn't mean "can't use language", which doesn't mean "can't communicate deliberately", which doesn't mean "can't understand communication". You might have preconceptions like "she won't be able to read until at least her first word, so there's no point teaching her": with autism, you have to throw that kind of reasoning out of the window, because there will be at least one thing that an autistic person is "unexpectedly" good at, and if they never get the opportunity to try, you'll never find that out.
If you want them both to have a chance at an independent adulthood, you need to start them on the relevant skills early. Don't save everything until they're 15, because that's a lot to cram into a short space of time. Autistic people don't understand things the same way allistic people do, and not everyone's learned the (culturally-specific) "translating from the allistic explanation attempts" skill, so explanation likely needs supplementation with lots of practical experience.
Example: when going shopping, start at the beginning of the process (going through the pantry / meal plan, identifying which things are needed, compiling a shopping list). Talk through what you're doing, and what your reasoning is. Try to make it a routine, where the same sorts of things happen each time, and decision points are exposited (e.g. "this time, we're driving"): routines are easier to understand, easier to predict, and more familiar, which can be comforting. Though, be aware that autistic people often have atypical sensory processing (https://www.autism.org.uk/advice-and-guidance/topics/sensory...), which might prove too distracting to concentrate on learning: you might have to go shopping during the quiet hours, if the supermarket is ordinarily too intense; or, conversely, a dim supermarket might not be engaging enough. (You'll know your daughters better than I do, but I'm partly writing this for the benefit of others.)
When stuff gets spilt, don't just clean it up: show them how to clean it (including where to get cleaning supplies). When getting breakfast, show them how to do it a few times a week, if they're not already doing it themselves. (Perhaps let them practice pouring measured amounts of washably-dyed water between various containers – plastic milk bottles, especially, are unintuitive near the top and the bottom.) Eight is getting a bit old for such things to be "socially acceptable", but fortunately, autistic people tend to care less about such things (modulo social anxiety), so if you don't say "practising these basic skills is for younger children and other people will judge you for it", that probably won't be an issue.
Abuse is always a concern, but most women have to deal with that sort of thing: these aren't unusual worries for a parent of two daughters to have! Society will be better when they're older. Just try to keep them out of environments where one small group of people is judge, jury and executioner, such as prison-like "assisted living" facilities, or the "care" of ABA practitioners (see: https://starvingautist.com/aba-good-intentions-are-not-good-...). (A good assisted living facility might be really helpful, though: it all depends on what each daughter's needs are when they're adults / no longer your dependents, which is hard to predict from how they are aged 8.)
You might find these stories about an autistic(?) man with limited speech, working in a Swiss police station, interesting. https://notalwaysright.com/no-accident-kboom-explode-on-his-... https://notalwaysright.com/no-neglected-post-on-his-watch/30... https://notalwaysright.com/no-lapses-in-security-on-his-watc... They're written for an allistic audience, but the depiction feels faithful: given the situations depicted, I imagine I'd make the same decisions as Peter did (if I had enough self-confidence to work that job in the first place).
They're also good depictions of autistic morality. Academic descriptions like https://www.spectrumnews.org/news/mind-blindness-affects-mor..., while faithful descriptions, tend to interpret this as "mind blindness", but really it's just having higher standards, closer to what Eliezer Yudkowsky would call "heroic responsibility". (https://aarongertler.net/heroism/ is probably a better description than anything Eliezer Yudkowsky's written.) This article writes:
> The man traveling in Africa who encourages a friend to swim in a pond after seeing other tourists frolicking there is to blame for that friend being bitten by a mosquito and contracting malaria, [autistic research subjects] say, just as the girl who builds an igloo out of snowballs is to blame when icy snowballs crash on her friend’s head.
This makes intuitive sense. Somebody who does not understand that mosquitos are common around stagnant or slow-flowing water such as ponds, and that malaria is endemic to many parts of Africa and can be contracted by mosquito bites, has failed to perform the most basic research, and it's negligent to provide uninformed advice about things to do. (Basing your recommendation off the activities of other tourists displays a severe deficit of theory of mind, but such groupthink is common among the allistic population.) Likewise, if building a structure out of heavy materials, you need to take into account the material properties of such a structure: practising engineering without a license is illegal in many countries, for exactly this reason (not that this heuristic is perfect: https://www.vice.com/en/article/n7jq98/man-fined-for-enginee...).
For some reason I can't explain, the authors chose to bookend this paragraph with:
> But the moral conundrums in the second set of experiments flummoxed them. […] In case after case, they assign blame to individuals who intended no harm, failing to distinguish between intent and outcome.
but any philosopher of ethics will tell you that this is an incredibly defensible position, and many will tell you that the standard allistic position makes less sense. Academia – and society in general – labels as a deficit what is actually just a failure to understand allistic nonsense that nobody ever bothered to teach.
It might be worth learning a sign language (ideally one used in your local culture), and/or investing in an AAC system (see https://www.rachelmadel.com/blog/stimming-and-aac for a common misconception).