I think mafiaprincess is right you need to go back to basics. There is a potty training article on this site on Information that I used. Hope it helps.
http://www.goldenrayyorkies.com
I have a yorkie purebred and have read a lot on these biewer and it's not what I would want. After reading up I found they are not reg. with akc either.
I am so sorry. The only thing I know of is the vet diets too but have known dogs to live years on them. Hope it all turns out ok. I have a yorkie to and understand what she is feeling.
I think they are both sweet breeds and should get along great. I know lots of people that have 2 dogs and different in size so that should not be a problem either.