New kittens - please help!

[SorryForTheRant]

Sorry in advance if this is long, looking for advice on how to settle two unrelated male kittens.

We took in two unrelated male kittens yesterday, one 11 weeks old and one 8 weeks old (will refer to them as 11 and 8 going forward). 11 arrived first, was here around 2 hours before 8 got here. Neither neutered yet but both will be as soon as the vet advises.

11 is very chilled, sat happily on us, seemed very comfortable until 8 got here. 8 is very playful, exploring everywhere, less interested in humans but desperate for attention from 11.

11 is way more stand-offish, and is now hissing whenever 8 comes near him. I know I've been an idiot as literally EVERY piece of info says keep them separate but I thought it may be different if they were both coming into a new setting, rather than one being settled if that makes sense?

I really want both to be comfortable, there are moments of promise where 11 will go up to 8 to have a nosey, but then immediately goes back to hissing. 8 just sits and takes it, will lie submissively, isn't afraid of 11 but isn't trying to be dominant either. Do I leave them together and hope they gel (bearing in mind it's been less than 24h so far) or separate them for now and try to reintroduce in a couple of days?

Thank you if you got this far!

It's pretty normal for them to be wary of each other in the beginning, but if you can see what areas of the house each of them likes to spend time in as their "territory", you could try to keep them apart a little bit from each other's space until they are more comfy. Eg. if one likes to sit on the couch and one likes to sit on the bed, keep the other off that area for a while until they are more used to each other.

Thank you so much for replying! We're trying to do this and on day 2 they seem a bit better, 11 is still hissing but he is now lying and showing his belly to 8 which I feel is a good sign as it's more like play fighting?

If you're around I would keep them together and just supervise. Separate at night if you feel uncomfortable leaving them alone though.

We have three unrelated cats and have always just chucked them together to get on with it - I know that horrified most posters on here though

We've never had a single fight or problem - the odd hiss, sure but otherwise they're fine. We always separated the newcomer when we went out or to bed for a couple of weeks just in case, but otherwise they've all lived together from day one with no drama - they're now 7, 6 and 2 and happily sleep together, share food and water and trays and bathe each other too!

Thank you @mountainsunsets this gives me hope! We've left them together overnight and they aren't harming each other, only hissing so hopefully in a few months I'll be where you are!

I wouldn't worry too much about hissing on its own - just make sure it doesn't escalate to growling and attacking.

Hissing is often just a sign of fear/uncertainty as opposed to full-on aggression. One of mine is a rescue and he still hisses if he's scared but it's never once escalated into anything more. It just means "I'm uncomfortable, leave me alone" - and the other two respect that and do leave him alone.

The only issue you may have is that if the youngest ignores the hissing as a warning, it could escalate into a fight but I'd say that's pretty unlikely in two kittens so young. I'm sure they'll settle down soon!

My 11 year old cat hissed at the kitten for 6 months. No violence just hissing.
Now they spend all day sleeping together and chasing each other round the house.
Just give it time.