OMG Irina, how awful for you (and Tabi!) I forgot to say my Chuch is 9/10 years old so i thnk i've been very lucky! Charlie, the newcomer, was the one shut in the spare bedroom,with litter tray, food etc, which i thought would be a nightmare after the life he was used to, but he was great from day 1-i expect that was due to knowing him from when he was a kitten! I'd go in every so often and fuss him-he wasn't interested in toys! After he's been here a week or so (?) i started wedging the bedroom door open with some cardboard so they could see each other but not get at each other! When Chuch went outside, i'd let Charlie have the run of the house (well, bungalow) so his smell was everywhere The day i decided to let them meet, i got my friend to come round to help (she'd got a feisty cat so was used to aggro, whereas Chuch was my first cat) She stood there armed with a brush and oven gloves, but Charlie hid under the bed and Chuch stayed in the hall! In the end, i had to do it alone the next day and i was terrified! It went really well tho-i think he'd been here about 4 weeks then (would have to check back on my 'diary' to be sure, tho')
I think you're gonna have to start from scratch, as if Fred has only just arrived, and shut him in a room, with her having the run of the house, then gradually, let them see each other through the wedged open door. I also had a Feliway diffuser which someone on CC very kindly sent me-that seemed to work wonders on calming Chuch.
Good luck again-i would hate to see them fighting, it must be so upsetting!