This is a tough one! You have the dogs in the very desirable state of being completely housebroken...they have learned the lesson that the inside of your home is NOT being acceptable place to relieve themselves...and now you may have to partially undo that. My guess is that they are very uncomfortable with the concept of having to go indoors...I have one dog like that, she has total run of the house both when we are home and away, and I think she would burst before she ever pottied in the house.
Is there any way at all that you could look at the dog door option with the door letting out into a secure, covered dog run that would keep them safe? (And also keep any unwanted visitors from coming through the dog door into the house!) Or if you have an attached garage, could you set a dog door into the service door between the garage and the house and put some sort of potty area in the garage for them?
If that doesn't work for you, is there a possibility of getting someone trustworthy (family member, friend, neighbor?) to come over and take the dogs out in the middle of the day? You could hire a professional pet sitter, but if it is something you need done daily, it is going to get expensive.
If the dogs do not like the "grass" pads, maybe try a litter box? They make doggy litter boxes, but I just use the large flat plastic underbed storage boxes (I breed, and I put litter boxes in the puppy pen for the pups and also for mom if she has to go). You can use any number of things in the box for litter...dog litter, kitty litter, shredded paper, newspaper, wee wee pad, etc. I just buy reams of cheap white office paper and run it through my office paper shredder, and voila, dog litter!
Good luck, I hope you can find a solution that works for everyone!