I just brought my 2 year old dog to meet her siblings for the first time since they were adopted at 3 months old. When they came in contact with each other they became angry and aggressive. My dog and the other dogs don’t act like this towards other dogs. Why did they act like this to each other?
There are many possible reasons why your dog acted that way. Since I am not a top expert in this field, I can only tell you what happened to my dog in this case. A behaviorist told me we introduced our dogs wrong. (Imagine that) My wife and I brought my female dog to her sibling's place and her sister was territorial. He told us to take them to a neutral area, where no dog will feel threatened. it is important to https://worlddogfinder.com/blog/dog-tips/puppy-and-dog-socialization (socialize) your dog from an early age, and you should do that if you haven't started already.
You can try introducing them again somewhere outside their home, and see how that goes.
Hope this might help!