I have a 4 month old yorkie and a 2 month old golden retriever. I brought home the Golden retreiver yesterday and it seems like they always wrestle and bite, so I keep them separated most of the time. The yorkie seems to be the more aggressive one and the golden is more submissive. I am worried one of them might get hurt, especiialy the yorkie since the golden is nearly triple its weight. Is the yorkie jealous or are they just playful.