Yes, more Harris

I'll not lie, this hasn't been easy. We knew Isla, 14 years old, and on her own with us since we rescued her 9 years ago, would probably not react well, but we thought it would be manageable. The stress for her, however, has been difficult to see - she's avoided the house as much as possible (at least she has the outside as a safe place), initially running out every time she hears Harris cry (he's quarantined in the spare room), and hissing and growling at any strong scent of him. There've been tears seeing her reaction, and even in 24 hours I've missed having my wee pal seeking me out.
But things have mellowed 'slightly' in that time so we're just taking it easy, following advice of TV cat behaviour chap Jackson Galaxy (honestly, the guy is cat rock n' roll), which all seems pretty reasonable and considered. We 'had' followed the advice from the shelter, which was to show Isla the kitten in the carrier when we first got back - not a good idea, as she hissed, spat, growled, then ran off. I don't think we'll get to a loving housemates stage, but as long as Isla can tolerate him, and gets back to being herself.... Before some new Feliway arrived tonight (the wonder of Amazon Sunday deliveries), which did seem to chill her out a fair amount, she had wandered up into my lap, and gave me a purr for the first time in over 24 hours.
For his part, Harris is the most confident kitten you could imagine, and is a wee snugglebug - seemingly adoring human company (he's currently clinging to my leg trying to get onto the laptop). I slept in here with him last night, and every time I woke up through the night there was a wee kitten face right in mine, with him tucked into my arm. He's a little fuzzball as well, already litter trained, and purrs constantly, so I don't think we're going to have any issues on his side.
Fingers crossed in a month's time or so (likely a couple of weeks at the earliest), the stress levels have dropped, and Harris is able to wander about the rest of the house.