I think it’s clear op that the house has lacked maintenace over the years, and it would appear maybe it’s been lack of finances, it would be unusual for example for someone to replace their bathroom and leave the ceiling like that through choice.
The house has become a renovation project. The dining room and garden room are fine, the kitchen liveable, and the bathroom upstairs ok, although both done low cost. The rest is a full on renovation.
Usually this is either due to lack of money, or inability to manage home maintenance, and for either of those reasons, it’s best to think carefully about how much you can realistically do.
Any botched touch up jobs are going to look awful, and very visible against the rest of the room. Fresh paint against old is very visible and a huge red flag the owner is trying to cover up problems. Plus if you don’t know what you’re doing, it will look even worse.
So unless you’re suggesting to throw some serious cash at this, I’d hesitate to go the route of doing anything much.
I’d simply get a magic sponge, clean all your paint work. Have a professional in to deal with the living room ceiling, and get a professional in to clean the carpets. Power wash the outside. Give it a good clean everywhere, inc internal doors, the shower head etc.
Then sell it as in need of modernisation, accept mentally that the new build estate is happening and buyers will know that, and that will reduce the value, and price it accordingly. Likely in the region of 300, but willing to accept lower offers.
Or stay put and accept it’s got to such a level you can’t command what you need for it.
Houses always ultimately escalate in value, unless they are not maintained, they they depreciate in value. And by more than the renovations cost. Add in a massive change in surroundings, Ie moving from open fields to overlooked and boxed in by new builds and the value depreciates even further.
I do feel for you as I think you’re in a very difficult position. It looks like you’re trying to scarper before the new build estate starts, and literally before the ceilings start to cave in.