Reasonably experienced cat owner here, but been a while since I introduced a kitten to an older kitten.
Cookie is our resident older kitten, about 9 months.
Biscuit has just joined our home in recent weeks - about 9 weeks but a little small because his mum was struggling a little. I still give him the odd drop of kitten formula.
Cookie has been generally welcoming and lovely. Licks him, makes a point of sharing. Odd hiss, but generally really nice. We did scent swapping from a distance and introduced smoothly. He adores her.
Just a little concerned she'll be too rough when they cat wrestle. Lots of chewing but no actual bites. No claws. He's not a bit afraid of her (actively seeks her out).
We use Feliway and my feeling is it's playful. Any tips on when to intervene and how to recognise when things are headed in the wrong direction?
Thanks for any help. Obligatory photos included!