Spod - I have been in a similar position to you, but unfortunately am not able to provide a positive resolution, but more some pointers for you. I think that there is a real shortage of resources for CT scans and suspect that is why they do not appear to be hurrying to get things done; also the fact that your dh's grandmother became ill at the weekend may not have helped, as not all the scanners/departments may be running at the weekend.
My grandmother had a stroke a few years ago and died shortly afterwards (about a week later)without regaining consciousness. She had the more unusual sort of stroke, a brain haemorraghe type of stroke, rather than a stroke caused by a clot. In view of her general poor health prior to stroke (bad chest/heart) she was not a suitable candidate for neurosurgery to treat the bleed. A stroke caused by a clot IIRC has a better prognosis, and drugs can be given to break down the clots. My mum and I had to push very strongly for a CT scan for my grandmother.
I would agree with the advice to push to get her into a stroke unit if at all possible. I think the best thing would be for you/dh/family to arrange to have a meeting with one of the doctors looking after your dh's grandmother to discuss prognosis/future care etc. I think you also need to make her pre-existing deafness/communication difficulties clear to the nursing staff, and how she would typically communicate before the stroke. Could your dh's grandmother write on a pad of paper/read a magazine atm?
In terms of care homes - I am not an expert at this but there are two types of residential homes - an ordinary residential home, and a nursing home which would be specifically registered as a nursing home, and so would have to have a higher level of staff than an ordinary residential home and would be geared up to providing more intensive nursing support to elderly people requiring a high level of care. I do not know the ins and outs of funding and finding places in such a home but there may well be difficulties ahead that other mnetters could give some better advice on.
Hopefully things will start moving a lot faster with your dh's grandma tomorrow, once the weekend is over, and all the departments at the hospital will be fully functioning.
Best of luck to your dh's grandma