For the potty training, you might want to take them out to pee frequently throughout the day, until they get the hang of things. They're probably just getting used to their environment and need to get used to it. You might want to try those sprays they sell at petsmart that attracts dogs to pee in certain areas. You could try spraying that on the potty pads and see if it helps.
As for the eating, my yorkie is a picky eater..he almost never eats the recommended amount of food per day...but he does drink a lot of water. Maybe you just need to try and different kind of food? That's what I did with mien and it has helped. Also, if you don't think they're eating enough, you can take them to the vet to see if it's somehting physical, or you can give them nutrical which is a food supliment (i think?) You can give them that when you think they haven't eaten enough.
Hopefully others will have more information for you.
If it ends up not working out for you and you feel you need to rehome them, one of my friends is looking to adopt a yorkie and I would probably be interested as wel, as Mr. Biggs doesn't yet have a sibling.
I hope everything works for you! And it was so nice of you to take those babies in!
