I'm glad you are seeing some progress, even though I am sure it is frustrating that it is such small steps. Given that he was seemingly completely handleable when you went to his breeder's to pick him up (I know you said he hissed but you were able to pet and pick him up without issue there?)... it seems odd to me that he hasn't settled more. Maybe it really does require a kitty friend. Normally I would advise keeping by himself until he was fully bonded but if he was more open to your Chartreaux then maybe just putting that cat in the room might calm his nerves? Maybe he is simply a very nervous personality and he feels so vulnerable as the little kitten all alone? I probably still would keep him in that room, but confine the Chartreaux in there too. If she is anything like my British Shorthair she will make a great nanny for your kitten. Generally, when I wean my kittens I put him in with them to start introducing them to other cats and he's been known to even allow them to suckle on them for comfort.
I wouldn't introduce all your cats though, and I wouldn't let him out of that room yet either. I honestly don't know how long this will take... and whether he will ever be what you consider "normal"... we are all individuals after all, and maybe he's going to be a sensitive one that is reactive and not so cuddly...
I wouldn't introduce all your cats though, and I wouldn't let him out of that room yet either. I honestly don't know how long this will take... and whether he will ever be what you consider "normal"... we are all individuals after all, and maybe he's going to be a sensitive one that is reactive and not so cuddly...