Thanks for the responses.

Yes, they are both neutered. Also, I do have a couple of Feliway diffusers running since getting Strauss. The incident happened in the backyard though - away from the influence.

Maybe Rescue Remedy should be the next step. Strauss is doing well with the others. Joxer is such a non-agressive guy that they have no issues whatsoever and Jan is annoying, but at only 8 pounds, Strauss just thinks of her as more of a pest.

I was just so sad when I saw those scratches on Sid's face and his bloody ear.

I plan to give Strauss plenty of time but ultimately if I have to choose between the two, well, it was Sid's home first. But don't worry - I'll do everything in my power to make this work and if I can't - I'll find a good home for Strauss - he won't be seeing the inside of a shelter.