Ok so your daughter is in a really bad position now as for the best part of 30yrs she’s done without support due to you not addressing her issues, which you say is down to you being disabled yourself.
Regards the PIP she needs support to be able to apply for it properly, from you and from citizens advice. As a starting point you can google ‘PIP form guidance’ which should show up multiple guides from disability charities as to how points are awarded and the descriptors. If your daughter doesn’t write at length regarding how she is at her worst, using the appropriate descriptors then she won’t get it. I really think this could be worth revisiting as it could avoid the need to sell the house and help her to be more comfortable. If she gets PIP there will be an uplift in a lot of other benefits she may be due too.
If you go to national/local autism charities they will help support her with work and assess what type of work may be best for her. Be aware she may have to take work that she is overqualified for to be able to cope with it. It’s likely her living situation is contributing greatly to her inability to sustain work if she is stressed out by the lodgers and so forth. Perseverance is key and being supportive, even if it just isn’t possible for her. It’s easy to slip into treating her as ‘normal’ as that’s how she looks, but she is a vulnerable adult and one that hasn’t had the benefit of proper support throughout her life so that leaves a legacy of trauma unfortunately.
Relative to her needs, there should be some indication as to the level of her difficulties in her assessment report, surely? Again, speak to an autism charity, they can come out and do a review with her and help get supports in place, I would advise that you steer this and are present for any meetings as you appear to be her primary carer.
Regards your retirement, I really do not know why you are wanting to squirrel away massive amounts in savings, especially if you live in England and care in the community is charged (it isn’t in all other U.K. regions). Fair enough in your personal pension. But keeping a big house or thousands in savings (unless you are a high earner with bountiful amounts), is folly - it will only be taken by the LA for care.
Bear in mind you can still have up to 16k in the bank and still get benefits. Regards a care home, if ever the need arises you put yourself in as temporary resident and stretch that out as long as possible (usually a year, sometimes 18m if a social worker is tardy with paperwork). That way it doesn’t cost. All you need is enough to get in the door of your home of choice then when the money runs out the LA take over.
Regards saving the house either sign it over to your daughter (early) or have her live with you as carer before you go into a home, than and/or her status as a dependent/vulnerable adult will save it.
Much more to this than I’m giving info on, you need to do a lot of research and see a financial advisor and solicitor for advice as to your pension/finances/will etc. before you do anything drastic relative to your daughter’s home.
Your detachment from her would be symptomatic of ADHD and you need to be aware of this. She is a vulnerable adult and you do have responsibility to her, particularly since she is largely in this position now due to your issues getting her support as a child.
All the best of luck with her and I hope you’re able to get some solid advice from professionals outside of MN.