Yes, Tiffany is Ricky and Bianca's daughter and neither is on the show. Bianca will likely never return as Patsy Palmer seems over playing Bianca and now happily lives in Malibu. I do think Bernedette/Tiffany are one of the stronger points in the show and it's been allowed to developed gradually as opposed to over night. I'd prefer them remain as friends though, as I can't bear the thought of watching Tiffany turn into another Sonia - a lesbian only when it suits her. I really enjoyed the scene on Friday with Kat and Tiffany in the vic talking about love and when you find it - it's moments like that which soaps no longer bother to do.
Kat's next chapter is potentially the most exciting thing about her. If they really make a strong attempt to move her on from Alfie and her sexual abuse from Harry, it would be a great start. She's a stronger character than Alfie and he brings her down. Jessie Wallace has been on fire this whole stint and the show is very lucky to have her back. It's been great watching Kat back in action working in the Vic recently, she really added some excitement to the place. I also see a really nice friendship developing with her and Linda - much more believable than the friendship Linda and Sharon have. I think it will be a while before they try to find her another man, but it would have to be someone totally opposite from Alfie. I also think Kat's at a stage where she can occupy a similar role to what Bet Lynch had for years on Corrie.
Letitia Dean is on vacation, hence why Sharon isn't on and the one decent story she's had in years.
Mel's return has a big failure, especially with today's news. She's been back for a year and has not been integrated with the rest of the show - she and her set are totally isolated and she has no other meaningful relationships. She just doesn't fit into this show anymore, and it will take a lot of work to make her happen again. I did hear Tamzin extended her contract a bit, so maybe it's to play out the aftermath of this story and she leaves. I won't miss her as this whole stint has been pointless as hell.