Help - integration advice needed

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Hello,

sorry, this is long as I'm trying to give as much info as possible.

I'm appealing to those who know more for advice.
we had 3 cats, 3-5 years old, all came to us separately (over 2 years) as rescue kittens.

We (perhaps unwisely but that ship has sailed!) have just acquired 2 more. Previous strays. Now neutered/sterilised. An older female (mum) who is gentle and is integrating well, I won't say anything more about her as she's not an issue! The issue is her son, a ~ 12-18 month male who is extremely friendly to humans, over confident, and thinks he owns the place already. He's the problem. They've been with us 3 days. They are mostly contained in a small utility (beds, litter tray, food, water in there) but we have been letting them out to have the run of the kitchen diner, then shutting them back in to the utility at night or to let our existing cats in. The idea being to give them a 'safe space' but work on integrating them. The utility is very very small - it's fine for a few days but we'd like to start getting them used to a bigger area. We've introduced them to all 3 of our other cats very briefly - with 2 adults with them, and with biscuits to distract them (new male is very very food oriented).
however, despite new male being an absolute softie with humans he is aggressive and defensive to our existing cats and went to chase them off when he saw them. When he did this we removed him and put him back in the utility, trying to enforce the idea that the kitchen was not his territory. Then yesterday I made a door error and one of our existing cats got into the kitchen when the new ones were having a run out and the new male went for her. We split them up very quickly, no physical damage but she's scared of him now.

over the years I've integrated cats a lot and I've never had this. Yes, hackles, noise etc and I'm not saying mine are best friends but I've never had a proper issue.

What to try? The literature says to introduce them somewhere where they can see each other - like either side of glass - we just don't have this set up. I thought about a dog crate but that's just far too small to keep him in for any decent length of time.
I've seen cat gates for doors but they would be high enough (or wide enough, but we could maybe put some together to overcome that). It's like I need a run that I can attach to a doorway to allow them to come into a bit of the kitchen so they can all see and get used to each other, do that for a while and then eventually try integration again once they've got used to that. Does such a thing exist (and does it cost a fortune?) . Any other suggestions?

🙏

Could you make a screen frame/ set up a roll of netting to seperate the kitchen from the utility? Tape it on to the door so they see and smell each other but are seperate.

You can get extra tall cat gates that like baby gates are adjustable for width - have a google. You can also get clear transparent screens that you could use as well, especially if the gaps on the gates are a bit too wide and let paws reach through. Also do you have a tall cat tree? A lot of aggessive behaviour comes from being scared, and being up high makes many cats feel safe and having places they can escape to is important for all of them.

Also, he is a young cat and probably has lots of pent up energy and needs lots of frequent playtime with wand toys and balls. Sounfs like you are letting them have the run of the kitchen but he probably needs you to actively play with him (my 5 year old loves being chased up the hallway!). Then try introductions when he's a bit more tired.

Also try feeding them either side of the door (and cat gate if you get one) and giving them all treats when there is no hissing.

I sympathise as its so hard when cats really don't get on. But it's only been 3 days and he is probably still very confused with all the change in his life so give it time - he might take weeks to settle down so be patient. But unfortunately some cats just never like sharing and prefer being 'only' cats so a tough decision may be needed at some stage. Cross fingers for you though!