I've not read the whole thread but you need to start thinking of care for yourself and your husband (and then your DD might get her head out of her arse and realise the situation requires change).
If you've not already had one, ask for a Carer's assessment for you and a Needs assessment for your husband. Get Social Services involved as they can be a great help and also get the house altered for your DH's mobility and cognitive needs.
Start to talk to the entire family about care needs and how things will have to be put in place now or at least, very soon.
Looking after someone with dementia is utterly exhausting, so you need to be ahead of the curve and implement things before they're needed or you will reach breaking point.
If your family are selfish arses, then you're going to be on your own anyway, so best you know sooner than later. If they're just fucking clueless, then this might be a useful wake up call that they will have to sort their OWN childen out now.
Work out what you CAN or WANT do and tell them. That's all you can do, if they kick off that's on them and given the amount of time and money you've saved them over the years, that would be very disappointing.