I do feel for you, it’s an awful lot to cope with. Unfortunately some relatives will always be like this. For several years I used to visit a forum for carers of people with dementia, where they were known as ‘the invisibles’. Sadly they are all too common and you’re entitled to feel upset and hard done by.
I’m assuming your gran will not be self-funded, in which case I think you’re entitled to ask social services to sort out a care home. Tell them you have no idea, wouldn’t know where to start, etc., and are unable do it., From all I’ve ever heard, they will be willing to leave it to you if it seems that you’re (albeit reluctantly) willing and able.
As regards clearing the house, I know it’s very time consuming, and will cost, but I’d just remove anything valuable or sentimental, and then get a house clearance co. in. Though you may like to keep a few things to make your GM’s CH room feel homely. We did for my mother, but TBH by that stage she didn’t really seem to notice or care.
One thing I’d def. say, though - people with dementia do often hide things - money included - in the most extraordinary places. It’s well worth checking everything that could possibly serve as a ‘container’ before getting rid. Inside coat pockets, handbags, cornflakes packets, teapots, inside books, you name it. A colleague of mine found £2000 stashed inside or between a pile of newspapers and magazines in the flat of an old uncle when clearing it. And my sister and BiL found a valuable ring (aunt had complained that someone had stolen it) wrapped in dirty underwear and chucked in the bin!
So do please be aware.
Good luck and all best wishes.,