Hi all.

Thanks for the answers. I've been looking up the deafness thing and I mentioned it to my mum who said she knew somebody years ago who's dog did the same when it went deaf. That dog lived indoors but still did it.
We've had dogs previously that went deaf in old age but, fortunately, they didn't develop the barking issue.

If I had my way, I'd find somewhere in the house to put them at night but, trust me, there is no way no how am I going to convince the parents, in particular the stepdad, to let them come in on a night. We have an enclosed insulated porch against the house but he doesn't even like them in there, says they leave a doggy smell which he hates and also the cats spend the night in there and we couldn't leave them all in the same place.
The kitchen floor is lino and Mist can't really stand up on it properly because her legs just slide out from under her. She can walk across the kitchen ok but if she's actually in there and has to get up from a laying position on it, she has such difficulty.

As for the shed, it was built as a potting shed and for putting plants in too and has windows all along the front from half way up to the roof so it's only dark in there at night anyway and she will be with Jess for the rest of the time. It is even darker in her kennel because they have carpet strips that hang down in front of the openings to keep out draughts and would also be dark in the house at night so there's no real difference regarding light levels.
She stayed in there last night and wasn't any worse than usual but her bark is much more muffled so it won't be heard by other people.
I cleared it out and removed anything that could fall on her or be dangerous.
I can mention to the stepdad about providing her with some extra light although light pollution on it's own will stop it being pitch black in the shed even at night.

I know it isn't good for dogs to be with humans 24/7 because this can cause seperation anxiety and over dependence. Spending the night on their own is better in that respect. I'd like to create more opportunities for them to be with me more in the day but it is so hard in winter when the garden is all saturated and such, you can't really spend any time in it. In summer, the dogs spend all day on the garden and flake out under the small tree on the top lawn out of the sun and I walk them during cooler times. At the moment, they can't spend time out on the garden because it's so wet and horrid.

fortunately, we've had it so mild this winter in the UK this year. Not a single snowflake around here put it that way. When I do bring the dogs into the house at bonfire, they just lay and pant and drink tons of water and I think this would cause Mist to not be able to hold herself for several hours at night as well. She'd end up doing it on the floor. At bonfire, I had to take them out on the lawn regularly throughout the evening.

When she goes for a walk, she wears a weather proof coat and, at home, she wears a kennel rug. Jess also wears a weather proof coat if it is raining when I walk them but Jess is very fit and mobile for her age. No sign of arthritis on her. Most people don't think she is as old as she is.

Also, being as she can still hear closer up or louder stuff, what about playing some music quietly to give her something to hear? I know that night time can be deadly quiet whether you're in the house, outside or wherever.
I'm not sure what I'd play the music with or how I'd power the appliance, lol. Would have to figure that out.