Neighbour cat fighting / hissing at my kittens

[Suzysuz]

I'm not sure on cat body language 😬
There is an older cat next door, used to wander in our garden periodically, not loads though.
We adopted brother-sister kittens who are nearly 1yr. They've been going outside since neutered and are enjoying the warmer weather and starting to venture further out our garden.

Neighbour cat has been coming and sitting in our garden a bit more, she seemed fine as she seems to happily sit near them (not too close), no smelling or interaction. But body language doesn't seem aggressive.

Tonight girl cat was close to neighbour in our garden and closely went near to smell her, neighbour cat did not like this, bit of hissing, bare fangs and flared whiskers 🙈
Clapped them apart, done.
Then boy cat was having a fun around the garden chasing a fly 😆, neighbour cat legged it across garden and went for him. Chased him into the hedge, I couldn't see but heard her hissing and boy cat gave a little cry 😩 managed to chuck a bucket of water into hedge, dropped the bucket in too by accident which scared off neighbour cat.
Boy cat took a good while to come out...

So is neighbour cat fine around them but doesn't want to be close or does she really not like them, but she was lay in garden, around them and seemed okay....

Or am I just massively overthinking because I luffs my precious furballs 😊

Boy and girl cat ❤️❤️

please don't throw water on other people's cats.

I'd leave them to it to figure things out for themselves - cats in close proximity "time share" naturally the space to avoid conflicts. Get s water pistol for the occasions you may have to break up a fight.

Eh? It's exactly what I'd do (and have done) when a non-resident cat is aggressive to mine or stressing mine out.

A super soaker can be targeted better though and after a couple of squirts in the vicinity of the uninvited cat they'll usually run as soon as they see it.

I thought water was okay to use to break up a fight?! I don't have a water pistol but will look to get one.

Just in case it's my use of the bucket - I assure you, it's a massively overgrown hedge, neighbour cat came out looking bone dry so they probably weren't where I threw it or given the hedge density it didn't even reach the floor!

Water is fine to break up a fight.
Cats are territorial. They're figuring this out. There will be hissing and probably a few spats.

Seriously it's fine to break up cat fights with water rather a bit wet than someone hurt

Is neighbour cat neutered? Bigger?

Neighbour cat is neutered, a teeny bit bigger but not too much in it really.
I know that that neighbour cat had issues with other neighbour cat 2 (other side) a good while ago and NC2 did go for neighbour cat and scared her off.
NC2 just seems to glare at our two, maybe one bit of hissing I've seen but otherwise they have seemed to stay out each others way so far.
Hopefully it is just sounding each other out and giving each other space 🤞

Chucking water on cats 100% the recommended way to break up a fight or scuffle. It won't hurt them and it means you can separate both animals without getting hurt yourself.

Why? It's a very humane way of dealing with cats who you want to either stop fighting or stop from coming into your garden. I've told all my neighbours that if they see my cat in their gardens and want her out, scare her off with water or acting loud and aggressive. Any cat with an ounce of sense will avoid these hostile territories.

You think neighbour's cat is in your territory but you're wrong. Your cats are in her territory and she's making sure they know it. I have an older female cat and all the young uns in the neighborhood know to steer clear, including my other one. They'll be fine once the rules are established.

That's interesting actually, I'd assumed neighbour cat didn't think of our garden as her territory as she never sat or lay in it, only ever wandered through right at the far back, maybe the odd sit there.
But it's probably likely that both neighbour cat and NC2 do think our garden is their territory, likely on timeshare as they dislike each other, and obvs now I've added my two so there are some socio-dynamics to be worked out...

Leave them alone, they’ll sort themselves out. It’s not likely they will actually injure each other at this stage. Your cats need to learn neighbourhood etiquette, it’s part of growing up. If you get involved, you will just slow this process down.
Cat squabbles always look and sound worse than they are.