When your brother arrives, leash Jonny up and all of you go for a long walk together. They may grumble at each other at first, but in a few blocks they will be sniffing the same things and soon walking side by side, then walk into your home with them together like it is the most natural thing. And they will be tired and empty! Before they arrive, pick up any "high value'" favorite toys or chews, anything that might make Jonny upset. Feed them separately, set them up for success by limiting things they might grumble about.
If the puppy is crate trained, or Jonny is, be sure there are crates where they can have some quiet time…a 10 week old pup would drive my older dogs nuts! Also allows you to separate them if Jonny is not happy to have a baby there.
If there is a dog park near you, you might meet at the park and let them get to know each other there, then go home together. But a nice long walk will really diffuse the tension, that is my experience anyway.
Anne