Try to find a food that is lower in protein...like 18%. Dogs that aren't very active don't need a higher protein content than that.

Also, feed 2 or three smaller meals a day instead of one big meal. It helps keep the metabolism going so that it doesn't get sluggish. Speeds it up in other words.

Do the dogs mind weather that isn't too great? If they do, maybe buy them waterproof jackets to walk in and make yourself take them out rain or shine. I buy waterproof trousers and coat for myself and wellies so that I am prepared for that type of weather in winter. Having had Border collies who couldn't care less about the weather, I had to take them out at least twice a day whatever the weather and had to take them for a decent walk too, especially when younger.
I also have flashers that clip to the dogs collars so that I can see them in the dark. In mid winter here in the UK, it gets dark at about 3:30pm. We only get about 7 hours daylight in the darkest part of winter so I always have to walk them in the dark on their evening walk and the flashers make them visible. I notice many dogs walkers who go to the same fields have also decided to get flashers for their dogs. It's great seeing all these flashing lights flitting around the field in the dark, haha.

At least you are making an effort to cut down their weight...not like my aunt and uncle with Mega, the obese JRT....