Disclaimer: I'm not the biggest fan of using pee pads. Both the SO and I have met a few pad-trained dogs that have problems down the line eliminating outside.
That said, to be honest, I don't see much (if any) training taking hold while the dog is home alone for 12 hours. I'll second what Katie1 said and see if you can get your mom to watch him while you and the SO are at work... and make sure that you're both on exactly the same page with training.
Assuming that you really can't go outside and you have to use a pee pad, this would be my approach:
Take him to the pad
extremely frequently; try every 20-30 minutes or so. Eventually (hopefully) he'll start to associate the pad with eliminating because you're not giving him a chance to do it anywhere else. When you want to need to leave him unattended for a bit, try putting up a pen and lining the bottom with the pads (this only works if he doesn't try to eat them).
If he's being stubborn and won't go—and you think he has to—be patient and wait it out. If he really has to go, he will... it might just take a while. Keep some high-value treats (bacon, a peanut butter-filled Kong, etc.) on hand and immediately—as in the
instant he's done eliminating on the pad—give it to him. Don't scold him if he goes somewhere he's not supposed to, only praise him when he uses the pads. When I took Leia home it was the middle of winter and I spent
a lot of time freezing my butt off in the snow and rain... you have it easy!
I would also go do a deep clean of the house with a good enzymatic cleaner like 3M or Nature's Miracle to make sure that he's not tempted to go in spots he's gone before.
I learned the hard way that not all dogs are equal when it comes to potty training. My SO's first dog (a cockapoo) was almost completely house trained within a month. Leia, on the other hand, was about 8-9 months old before she was reliably house trained.
Hopefully this helps... it's a frustrating and long process for some, but you'll figure it out!