I'm pretty certain that there's not much I can do, but on the off chance...
We have a smallish female, spayed cat. She's three.
Shortly after we got her, as a kitten, next door got a massive adult tom. There were a few spats once dcat was out and about, but it was ok.
18 months ago NDN got two more kittens.
Now the two ganging up on dcat.
It is getting worse - the young tom literally sits outside staring through the cat flap. They were coming in and attacking her to take her food, so we changed to a microchip flap.
If dcat goes out she gets jumped by the pair of them. It's got to the point that our clean, cat flap using, cat is now peeing in the house instead of going out. I've had to get a litter tray because of it. If I leave my back door open they strut in, eat the food and use the sodding tray meaning dcat won't!
Keeping the door shut isn't really an option - we have dc who are in and out and whilst old enough to be in the garden alone still need to be within earshot.
Any suggestions at all will be welcome. I'm even considering rehoming because it's obvious dcat is miserable. 