If anyone was curious how we introduce our new pups, especially because our dogs are all rescues and have no known history of puppy interaction. We spend 3-5 days where they can see each other but there is a barrier and gradually as they become used to the other dog we decrease the distance the dogs need to be from each other (before they are introduced.) We also give them treats for being around their new siblings when they are calm (still with the barrier there, but then they can associate the pup with treats). Thens we go on a walk on neutral ground and the dogs meet up, say hi and continue on the walk! Not perfect but it's how we have gotten away with relatively few squabbles. It takes a long but it is a lot of fun to have so many dogs& it's funny because they get along a lot better than a lot of human siblings do!