Just updating. I've stuck to my guns and despite more than 10 phone calls to the home phone in the last two days, I've not put DP on the line. DSD and I have exchanged messages in which she's tried emotional blackmail yet again (why are you trying to keep me from my dad?). Anyhow, I think she's finally figured out that the manipulation isn't going to work and her last message said she would apologise the next time she called the home phone. I know it will be a token apology but I'm willing to accept that. If she steps out of line again, the consequences will be the same.

I've also arranged an appointment with a counsellor for DP and I to talk about everything that's happened in our step-parenting journey and how we can move forward.

I've also done some reading which has reassured me that what we've experienced is very, very common.

I found this info on Daddy Guilt Syndrome and how it affects step relationships very informative

Donna Estes Antebi: When Guilty Father Syndrome Threatens Your Marriage