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If you are concerned, lock the other dogs up while you are working with the pup. I wouldn't be too worried about bad habits. It will be nice having other dogs to wear the pup out as well.
It will not be enough to just kennel the other dogs while training. Generally you want the retriever training to be highlight of the dog's day. If the dog is having more fun playing with the other dogs then it will be tough to compete with that. Basically to do high level retriever training you'll want the dog to be attached to you and mostly ignore the other dogs