My SO's daughters are older 20 & 16. I met my SO when they were 15 & 10. At that time there was parental alienation, spying, and false accusations of abuse.
I didn't trust, let alone like his children back then (puppets of their mother) and they didn't like or trust me (thanks to uBPDmom's lies).
I met his daughters in our second year together and have now known them for five. Each year our relationship improves and gets more comfortable. Today it's very friendly and easy going. Don't get me wrong there are still little bumps in the road once in a while but no more than any relationship you have with someone.
I've discovered that I have a lot in common with each of them and they seek me out when I visit there house, just like my son will seek out my SO when he comes to our house.
Both girls currently have very little contact with their mother by their own choice, but I would also support a decision to see their mom more if they wanted too. This site has helped me see from different perspectives which has been incredibly helpful in understanding the dynamic of my SO's family.
Things can get better for our (step) kids and we the step parents I think are a big part of that change. We bring in a different perspective on things both with the kids and the non-parent and we can change the dynamic and dysfunctional patterns that were previously in play.
So kudos to resilient kids, their non-parent and us!
Panda39