Ideas For Stopping Aggression In New Cat??

So my roommate recently adopted a 3 yr old neutered male. I have 2 spayed females ages 2 yrs and 9 months. Anyway, I used the guidelines for introducing new cats etc for the last 3 weeks. Last week we started gradually introducing the cats (one at a time) to each other. There was a little hissing and batting, but nothing too concerning. Then we brought all the cats in together once I was comfortable that they were not too aggressive. The 2 females mostly ignored the male and he was curious, but tended to back down if one of them hissed at him. However, the other day, I had them together for about 30 minutes and the male suddenly started attacking the kitten. I quickly separated them and put him back in his room. Now if I put them together the first thing he does is back her in a corner and try to attack! What should I do? He's very big comparatively, and I'm quite frustrated because everything seemed to be working well. I feel bad for him and don't want to keep him shut up all the time, but I also want to avoid injury to any of the cats. Any suggestions? Feliway?

Maybe you need to start over with just him. I think you might get better results with a one-on-one introduction. Put the other cats in another room when he seems like he's ready to meet the new kitten again.

I did introduce them one-on-one and they got along fairly well. They were even doing well with all of them together. It's just in the last day or two that he's become aggressive towards the two cats. I did try them again one-on-one thinking he was being overwhelmed and he tried to corner both cats by themselves. I guess that's my question. Is there a way to deter him from being overly aggressive towards the other cats?

Have you tried keeping him occupied while he's with the other cats? Playtime? Treats? The only way to deter him right now is to divert his attention to something he'd rather do. Hopefully the result of this is to form a positive association with being around the other cats. Remove him the instant he gets aggressive.

I don't have much confidence in Feliway, although some people claim it works. I've tried it and it didn't for me.

I wonder if it is real aggression. Myself I quess he is fighting for a place in the ladder! In the beginning he was apparently lowest, being the nowcomer. Now he wants higher up.

If so, the usual advice is to let them make their roles themselves, as long they arent fighting for real.

Make sure there are some shelves, shelters and hiding places, so the loosing cat has somewhere to retreat.

Sheltered sleeping places, etc are always good to lessen the stress pressure on cats.