I added Stryder when Kiba was 18 months. Tsuki and Lincoln came when Kiba was 4.5ish... Stryder was 3. And NoName was added into the house when previous dogs are now 7,5,and 2.5 (x2). Kiba wanted (and tried) to kill Stryder when he first came home. After living with other dogs and then added more they really stopped caring when other dogs joined. And they still play and get along just fine.