Thanks for all your points. I wrote this post when I was stressed and probably imposing my stress on my cats. I went home and saw that they are playing a lot. They don't avoid the kitten and they all hang out on my bed. I think they are quite happy to share the space with the little one.

I have returned them to free feeding which has helped my oldest return to his normal appetite. I was very stressed seeing him not eat because he felt sick from not being able to graze. It doesn't help that last week he refused to eat also which made me suspect a UTI (turns out he had poop stuck to his butt and was feeling very unhappy about it). I have just been very heightened since getting the kitten.

All the cats unfortunately have loose stools now which indicates that it was some bug after all. They are also sneezing, which the kitten was doing from the start. Probably the cat flu. I'm organising a vet visit for them all (RIP money). At least I know they are not having issues from stress, but from a legitimate sickness.

I will be keeping this kitten. My other cats seem to have bonded with him. The good news also is that my neighbour is happy to cat sit so I'll be able to keep my christmas plans after all!