I think we're continuing to make some progress. After limiting Izzy and Matilda's visits to a neutral room, we allowed them access to the upstairs hall and landing. Unfortunately, this is an area that Matilda also has some access to when she's not otherwise sequestered in her room. So, she exhibited a bit too much territorialism. I finally decided to let her loose in the main area of the house, the area that is now saturated with Feliway thanks to two diffusers. So far, the visits have gone well. No fights and a minimum of hissing and growling. Izzy follows her though and doesn't let her get out of her sight. Henry is mostly uninterested. I'll feel a lot better if and when Izzy grows less obsessed. It doesn't help that Matilda demands near constant supervision as is. She gets into everything and is a fearless climber.

I'm still just holding my breath about this. If it's truly not a good situation for them, I'd prefer not to force it, but it's hard to know what's reasonable to expect at this point. Ever the optimist, I ordered some Feliway diffuser refills. I do think it's taking the edge off their aggression. I'll have to order a third for the basement litterbox area if we ever make it that far.