I definitely feel for you...I'm keeping my mom's dog for the week because she dislocated her arm, and she's WORK. She's a 5 year old Yorkie mix, and she doesn't like anyone but my mom, my sister, and me. She's very picky and sometimes agressive to my Yorkies when they get too close to her chew toy or her food bowl. Sometimes it makes me crazy!
And I have to care for my sister's Yorkie Chloe all the time too, and she was raised by my mom as well...
Let me just put it this way...my mom COMPLETELY spoils them with no discipline, so when they come to me they don't want to listen. My mom is always commenting on how well behaved my dogs are, and I try to tell her in a nice way that you have to have rewards and punishments, the same as you would with a child. Now, I'm not saying I severly punish or hit my dogs, I would NEVER do that...but sometimes a loud clap and finger point and a loud NO are in order! All I have to do now when I see them doing something they shouldn't is say, "NO!" very sternly, and they stop immediately, but let me tell you, it took work! It's very hard when you're caring for someone else's dog who isn't as well behaved as your own...just the same as it would be if you were caring for someone's children. So, I feel for you, and I hope the diapers help! That's what I was going to recommend! Good luck!