New dog, need dog food advice!?

I have an adult female pit bull terrier and I just adopted a 5 lb (or less, she wont go to the vet till next week) yorkie mix. (that looks more like a chihuahua) Anyways, I feed my pit bull Diamond Performance. She does great on it, my vet says stick with it, plus she loves it. However, I obviously can't feed... show more I have an adult female pit bull terrier and I just adopted a 5 lb (or less, she wont go to the vet till next week) yorkie mix. (that looks more like a chihuahua) Anyways, I feed my pit bull Diamond Performance. She does great on it, my vet says stick with it, plus she loves it. However, I obviously can't feed this to my new little "purse dog" (lol). So I'm debating on what to feed her. I'm thinking about Royal Canin, but honestly, I'm not sure, for one, she's not a full blooded yorkie, for two, it does NOT look appetizing, and three, it is CRAZY expensive. I'm also thinking about Science Diet Small Bites. Isn't science diet usually highly recomended by vets? My vet says my pit bull is doing great on Diamond, but they do sell Science Diet in the office. Third I'm thinking about IAMS small breed. I know its not a premo brand, but a lot of people I know use it without any problems. So if anyone wants to offer their thoughts on those three, that would be great! Also, I want to know how to keep them from eating eachothers food. I've never owned a small dog before, but I know that I don't want her to develop a weight problem. I don't want my pit bull to hog her food either. The yorkie mix will totally share with her! I don't crate my dogs, so I really don't have any way to confine them, and I dont want to feed them seperately in the bathroom. lol. Oh, and I'm not going to continue the food she WAS on because it was the cheepest offbrand dog food in the world. (definately not high nutrition) Thanks in advance for any thoughts, tips or tricks!
Update: More info! The dogs get along great, they love eachother. Honestly, I was more worried about the little dog chasing our cat! but they get along beautifully. We don't free feed. We feed small amounts 3 times a day.. Thanks for everyone who has responded so far! She's sleeping in a little basket right now,... show more More info!
The dogs get along great, they love eachother. Honestly, I was more worried about the little dog chasing our cat! but they get along beautifully. We don't free feed. We feed small amounts 3 times a day.. Thanks for everyone who has responded so far! She's sleeping in a little basket right now, so cute! Of course the pit bull is fighting my husband for the bigger side of our queen bed!!!
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