Are my cats getting along or not?

[CatCatastrophe]

Introduced a new cat into our household this weekend - he was initially terrified (see other thread!) but quickly reverted to being the confident cat I'd seen in his previous home (a multi-cat household where he was known to be friendly and enjoy playing with other cats). One of my existing cats has always been friendly around other cats and my hope was the two of them would get on - they're both 2 year old boys.

They spent a day chirping at each other from the other side of a closed door, then my existing cat managed to barge in to the room with the new cat in. They met with nose bumps and chirps and had a good sniff of each other.

There's been no hissing or growling, bottle brush tails or anything. However they have been fighting. I THINK this is play fighting - both have instigated it, I'm not seeing any claws out and when it stops they are fine with each other - curious but calm.

Is this OK? Should I let them continue to 'fight' or do they need more gentle introductions?

Yes this is normal.
I have three cats all siblings.

They "fight" but are not hurting each other.

It's hard to say from your post.
Play fighting can look quite physical - two of mine (sisters) play a sort of chase and fight game. One enjoys it more than the other I suspect! There's a lot of thundering about and wrestling, sometimes a bit of squealing if it's got too rough.
But they definitely get along. They spend time together, they eat together, they sleep adjacent, sometimes piled in the same bed.
How are yours towards each other generally?

Sounds like play to me - my youngest two will tear around the house like idiots then curl up in a ball and sleep!

My rule of thumb is that as long as there's no growling, hissing, flying fur or injuries then it's just play. I'd also keep an eye out for puffed up tails and flat ears as they can also signify aggressive behaviour.

But if they originally greeted each other in a friendly way then it sounds like they're fine - my three are the same. Met on day two and within 24 hours they were washing each other and playing 🥰

That's reassuring to hear - I wasn't planning on introducing them to each other so quickly but they were quite eager to meet!

If they'd known each other for longer and I had a good sense of their relationship I'd definitely interpret it as play fighting, but given I've not got that much else to go on I wasn't really sure whether to see the behaviour as a positive sign (play) or negative (jostling for position/fighting), and whether we'd rushed the introduction a bit.

They've just come into the same room again and given each other a little lick and both acting very relaxed so it seems very positive!

They have accepted one another, but that doesn't mean they won't get on each other's nerves!! It might be worthwhile supervising mealtimes closely, so that there is no prospect of feeling threatened at all, which might cause friction. Make sure there are plenty of sleeping places, at least one more place than there are cats, and keep litter trays really clean too. Some will share trays, some won't.

You can get Feliway for multi-cat households, and that works well with ours.

Even two brothers, which we have had a couple of times will bite each other from time to time - not full on but still annoyed. They are cats after all and get annoyed with each other from time to time.

Sounds like yours are doing ok really and the odd spat is normal.

I go by the theory of no blood, chunks of fur or howling = play.

Can look pretty nasty, then 2 minutes later they are curled up on the bed together and/or grooming each other.

If they're grooming each other and greeting each other happily then I don't think you have anything to worry about :)

Mine look like they're killing each other sometimes lol.

There's been a tiny bit of fighting again this morning - I still can't quite work out the dynamics of it. I think it might be a bit of trying to work each other out and establish who is dominant but they're both inherently friendly cats so it's I think it's more friendly sparring than actual hostility. We have a feliway plug-in so hopefully that's helping.

I'm six months down the line and still not sure OP!

I think it's generally pretty obvious when cats are fighting - noise, flying fur, claws, teeth - IME it's very different to play. Play can be noisy but the claws are retracted, they bite but don't draw blood, the don't rip fur out, nobody walks away injured and they go back to "normal" straight away afterwards.

Play is also very even as a general rule. They should (ideally) take turns - one will roll on their backs, then the other. They'll take breaks. They will both "bap bap" with even strength, and if it involves chasing, they'll take it in turns. Likewise if it involves furniture, they'll alternate who has the "upper hand".

If I think things are on the "edge" I will break it up and they've never not listened - just a brief "ah ah" or "oi!" or a couple of sharp claps. If you can't break it up then I would potentially start to be concerned, though.

General rules on thumb is if they aren't making noise while 'fighting' then it's play.

Can look quite rough and aggressive but mostly my two would tumble around pretty much in silence.

If it got too much one would yelp out a little and they'd stop for a while then either restart the wresting or go to sleep/wash each other/cuddle.

Sounds like yours are doing incredibly well for being so newly introduced.

Mine fight and it isn't play but neither is it fighting. More daily communication.

Being irritated with each other while waiting for dinner- fine.

Obsessively hogging a door way or stairwell- not fine.

Hissing- the collar of calm comes out until the stressy one manages to behave again.