[ZenGum]

Hi Miss Helm-friend!

How are your wounds? If swelling persists for four hours, consult a doctor.
Seriously, as a cat owner, I assume you've been scratched plenty, and not had a reaction. That is kind of strange. Monitor closely.

Psst, Jim ... if she starts miaowing ... be afraid.

I've been a cat-owner often, but I have to say that introducing an adult cat into a situation with two other adult cats is outside my experience. We're brought kittens in, but they obviously fit in at the bottom of the social structure. Maybe some cat psychology is needed.

I've known two ginger cats. One, ginger /white like yours, had a bit of a mean streak but learned to not mess with the humans. The other, a pure ginger who belonged to a friend of mine, would snap from demanding very affectionate cuddles to full on attack with bite+claw+claw+rake+rake in the blink of an eye. Drew blood from me on two occasions. After considerable efforts (and nasty scratches on their daughter) my friend had to make the hard decision. The SPCA took the cat and said they would offer him for adoption for one week, and then euthanise him, but wouldn't tell my friend what had happened, either way.

Don't race for that option, of course, and now that you've had him snipped he might settle down. See what you can find about cat social psychology.
Come to think of it, New cat has had a pretty rough few months. Not surprising he's having trouble adjusting.