Let Sage and Ryker interact, it will build a bond and establish a good relationship between each other, no matter who will be the more dominant as they both mature. However, do not let Ryker overstep the mark with you. You must take control of him.
Harry and Lola sound very similar to your 2, Harry was and still is a very dominant dog, Lola is submissive and really easy going. I always allowed them interaction, they are never without each other and this helped build their relationship.
Yes they have had and still have 'words' with each other every so often and Lola has only seriously disciplined him a couple of times - when he went near her food bowl and annoyed her too much, and he was better for it.
Now, Harry is 3 and Lola is 5 and Harry is the dominant one between them, sometimes the older one will not be the dominant one because even though they are older and therefore suppose to enjoy right of passage - if they are not naturally dominant and the younger one it, then they will fall into their roles very easily, far better than a dominant younger and older one.
So, if they get on and enjoy each other, let them play and find their roles in the pack together, they are going to be together for the next ten plus years.
if your GSD is eating and eating and eating and losing weight - please consider testing for EPI.
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