Dogs barking

I don’t think letting them out is a good idea, although tempting for the poor dogs. Anything could happen to them.

I take it you're not in England? (It's too cold for dogs to be outside all day) Ring an animal welfare place and say you're concerned. OR go round, open the garden gate, and let them out.

Yes, we had a problem years ago with neighbours at the back of us, the poor dog was shut outside all day while they were at work. Environmental Health Dept. at the Council were not interested at all.
Had we realised so many neighbours were distressed by this we could have banded together and spoken to the owner or demanded more action from the Council. One neighbour used to take the poor dog into her house occasionally.

Have you contacted other neighbours at all? Strength in numbers.
Poor dogs, perhaps the RSPCA might do something, if only to have a word with the owners; leaving dogs outside all day in this appalling weather is cruel.

The only way ours was resolved was when they moved away (it was a rented house) but we could still hear it barking in the distance for a few years afterwards.

We are in the same boat with our neighbours 4 dogs, why do they keep them if they are at work all day?. I know it is time consuming but keep a log for a week or so and submit that to the council.

Why on Earth did they get the poor dogs in the first place. I’d try again with the recordings and perhaps mention to the owners that the incessant noise is upsetting to you. Are there any neighbours that are also upset by it? The more complaints there are the more likely the council will intervene. Hope you get a resolution to this.

Are the owners aware? If the barking is when they are out then they may not know about it.