Hi Aloise,
I've not had the exact scenario - but I had my boy Tazi and aged 4 we introduced 5 week old Nuggie. Tazi didnt enter my living room for 2 weeks. The third week was spent "spying" from a far with much hissing and spitting. He then attacked poor Nuggie to the point we didnt leave them alone until nuggie was bigger and able to defend his poor self. Next thing they are sleeping together and Tazi took on the role of Daddy & Brother and did a grand job.
Then due to circumstance many years later, I had to stay with my mother for a few weeks, who also had a young cat. Nuggie growled for the entire few weeks and stared at poor tiger. Taz however, took it in his stride. They had the stare off, established who was boss and got on really well.
I think it is because, Taz was an old hand at "looking out for the new" and protests didnt make them disappear lol He was also never phased by animal visitors and looked out for the cats in my street. Beau has probably thought the same, took a deep breath and decided to make sure Chilli is looked after - because its his job. Also Chilli is a pretty girl so he might have a bit of crush too!!
Nuggie is still a grumpy old man. Loves his mammy & his brother and thats the end. Tazi passed away a few weeks ago and nuggie is feeling it and has always had a companian, especially as i work. I'm thinking of bringing a new companian in sometime after christmas.....I sense he may do what Beau did with George and move outside for 3 months!! lol Poor old George is at the same "accepting strangers" stage as Nuggie. George has had his status compromised, but he'll get there in the end!! xx
Sorry if its not much use!! xx