I don't know if you should let the dog share the cat's litter box - dogs love to eat cat litter and obviously it wouldn't be good for them!
I've seen a puppy starter kit with a litter box and pine shavings.. you could just use newspaper or those training pads (they get expensive though). The thing is, once your puppy goes in one area, it wont' go there again so you'll probably end up with mess on the floor. Maybe you need to seclude them in an area and put a few pads down.
Is there anyone who could just come in and let them out mid day? It's hard to housetrain a small dog because the area which they consider their den is smaller than a large dog. So if you are considering housebreaking them to go outside, it will be difficult to go from the pads to outside. Better to start them going outside. If you can have someone just to even let them out to pee, then that would help.
I would agree with the others however, in that maybe you should consider an adult pug from a shelter. Some breeders even sell adult pugs when they retire them from breeding.
