Getting a Chihuahua puppy with a Great Dane and Mastiff already at home?

While you CAN put a Chi with two big boys, I wouldn't suggest getting a puppy. Having such enormous elders would cause him to grow up very insecure. If he were already grown, he would already have his own attitude and could more easily imilate to being 'the new kid on the block' than if he had ALWAYS been only the underling.