Advice on fostering kittens when one cat isn't happy about it?

[cats4ever]

The diffuser should go close to where Pixel likes to spend most of her time. Amazon has the best prices for the diffusers.
I hate to mention this, but you said that your older kitty started picking on Pixel, and he's getting thin. Both of those things might be signs of a health issue.

[Sowa]

I've taken him to the vet for blood work and tests. They said there is nothing wrong with him. He used to be really fat, around 18lbs. He's now around 11. This has been over years he lost that but the vet said the blood came back fine. He's not aggressive he just swats at her and chases her but not hissing and growling. I was thinking it was maybe she was acting a different way that has him doing that.

[Sowa]

He also used to sleep all day and now he plays with toys which he never really used to. I actually thought he looked more active. People tell me he doesn't look 14 at all

[cats4ever]

I'm glad that Shadow checked out ok. I'm sure that the weight loss helped him being more active.
And you're probably right that he's reacting to Pixel's different behavior.