Freckles & Doubt

I found a really good article on introducing a new cat at http://www.catbehaviorassociates.com/how-to-introduce-a-second-cat/, and was very careful with the sanctuary room thing and gradual introductions - they spent a couple of days on either side of a glass door, and being allowed into rooms individually in series so they got used to each others' scent. Also, Feliway! but the catnip thing really seemed to work in terms of them being within a metre of each other and not growling, when that distance would usually produce growls in the absence of catnip. The article suggests positive reinforcement and reward with lots of treats, but I didn't try anything beyond the catnip. You sound as though you've negotiated most of the adjustment process, though, I hope they take those final steps quickly!