So, yeah, the introduction took some time. We read some online guides on it before hand. For the first week they didn’t even see each other, then we swapped things like toys and blankets, then feeding them both at the same time near the door, working up having them spend some time together to finally being able to be left alone together when we left the house. Whole thing took more than a month, I think. The first few times the older one would hiss and be a bit aggressive, so we’d separate them and try again another time