oh poor zeus, you and family! I'm serious, exactly same thing happened to our family-dog, mocha. I knew no better back then but now I do.

I think re-training is best for now if you haven't tried yet, take him out every 2-4 hours, (depends on how often he went inside the house) don't let him back in until he does his business at 4th or 5th going outside. praise with his favorite toy/treat/food/whatever after he did, of course.

as for night, maybe could you have him crated in your room, and as soon as you hear him moving, take him outside immediately? or at least get up every five hours for now, then lessen hours by weekly if doing good. have you done that so everytime after you saw him peeing inside anyway? you should, but impossible since you're out a lot, right?

a lot (pretty long) walks would help extract his digestion/intestines to go sooner and relax better once back home.. how much does he drinks? sometimes exceed water isn't necessary, maybe a big bowl a day? would less his "I gotta go!!" ..

did vet says nothing about behavior issues? I know there's a lot of that in cats, but in dogs too? hmm. I mean, most? anyway, hope a solution will be found soon and you all live happily ever after!