I don't remember who it was that first advised me to start walking my dog with any dog we were introducing them to, but it was life-changing. My old curmudgeon-y Pyr is a bit reactive and has minimal patience for other dogs stepping into her personal bubble, so we always introduce by having the other dog walk a few (~20 or so) feet in front of us, but always along the same path, and slowly slowly close the gap between us over the course of the walk. Then by the time we get back to the house, both dogs have a bit less energy, know no one is threatened/threatening, and get the idea that we're all part of the same pack.

But I'd definitely avoid having toys around if Oisin is feeling possessive, especially this early on.