What about to a smaller, less busy city, with more opportunity for days out? IIRC CO serve a number of cities throughout the UK - Edinburgh or Glasgow, Cardiff, even York (going to MAN, then the direct train through to York) or arranging a taxi pick-up from MAN.
It might then be possible to get onto some of the daily coach trips organised by companies like
Wallace Arnold who are used to taking seniors around, while staying in a good hotel with the concierge to help them out if necessary. The smaller cities are easier to get out of, so might be a better option if they do want to see a bit more than a city?
Just a thought